Zero tail and unique word based waveforms for DFT-s OFDM and OFDM

ABSTRACT

Methods and systems for operation in a wireless network are provided, the methods including receiving modulated data symbols and zeros in a frequency-domain, and mapping in the frequency-domain the modulated data symbols and zeros in an interleaved manner to sub-carriers within a resource allocation. The methods and systems further include generating a time-domain data signal based on the mapped sub-carriers, and generating a time domain cancellation signal by sign inverting and repeating a predetermined number of time-domain samples at a tail portion of the data signal. The methods and systems further include combining the time-domain data signal and the time domain cancellation signal to generate an exact zero tail data signal such that the exact zero tail data signal has a zero tail length equal to the predetermined number of time-domain samples, and transmitting the exact zero tail data signal.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/777,761 filed on May 21, 2018, which is the U.S. National Stage,under 35 U.S.C. § 371, of International Application No.PCT/US2016/064196 filed Nov. 30, 2016, which claims the benefit of U.S.provisional application No. 62/262,649 filed Dec. 3, 2015, the contentsof which are hereby incorporated by reference herein.

BACKGROUND

In order to meet the high data rate required for the next generation ofcellular communication systems, the wireless industry and academia havebeen exploring ways to leverage the bandwidths available below-6 GHz andabove-6 GHz frequencies, e.g., at centimeter wave (cmW) and millimeterwave (mmW) frequencies. The large bandwidth available at thesefrequencies may provide enormous capacity improvement for user-specificdata transmission.

One challenge of using above-6 GHz frequencies may be characteristicsrelated to their propagation which may be unfavorable for wirelesscommunication, especially in an outdoor environment. For example, higherfrequency transmissions may experience higher free space path loss.Rainfall and atmospheric gasses, for example, oxygen, may add furtherattenuation and foliage may cause attenuation and depolarization.

Narrow beam patterns, which may be used to counter these losses, maypose challenges for a base station (e.g., eNodeB) in deliveringcell-specific or broadcast information. As a result, initial mmW accesslink system design may focus on cellular system procedures that enableadd-on mmW data transmission (e.g., at least downlink transmission) toan existing network such as a small cell LTE network. Outdoor mmWcellular networks may be feasible through the use of beamformingtechniques. In addition, a large number of reflected and scatteredmultipath components (MPC) may be utilized to facilitate the mmWcoverage in non-line-of-sight (NLOS) conditions.

SUMMARY

Methods, apparatuses and systems for operation in a wireless network areprovided for transmitting and/or receiving an exact zero tail datasignal.

According to an embodiment, method implemented in a wirelesscommunication device includes generating, by at least one processor, adata signal, including mapping, in a frequency domain, a plurality ofdata symbols and a plurality of zeros to a plurality of allocatedsubcarriers in an interleaved manner such that the plurality of zerosare mapped to empty subcarriers of the plurality of allocatedsubcarriers interleaved among data subcarriers of the plurality ofallocated subcarriers; converting, by the at least one processor, thedata signal to a time-domain; selecting, by the at least one processor,a plurality of tail time-domain samples from a tail portion of theconverted data signal; generating, by the at least one processor, acancellation signal from the selected plurality of tail time-domainsamples; generating, by the at least one processor, an exact zero taildata signal in the time domain by combining the cancellation signal withthe converted data signal such that the tail portion of the data signalis canceled; and transmitting, by a transmitter, the exact zero taildata signal.

According to another embodiment, a method for transmitting an exact zerotail data signal in wireless communications includes receiving, by atleast one processor, modulated data symbols and zeros in afrequency-domain; mapping in the frequency-domain, by at least oneprocessor, the modulated data symbols and zeros in an interleaved mannerto sub-carriers within a resource allocation; generating, by the atleast one processor, a time-domain data signal based on the mappedsub-carriers; generating, by the at least one processor, a time domaincancellation signal by sign inverting and repeating a predeterminednumber of time-domain samples at a tail portion of the data signal;combining, by the at least one processor, the time-domain data signaland the time domain cancellation signal to generate an exact zero taildata signal, such that the exact zero tail data signal has a zero taillength equal to the predetermined number of time-domain samples; andtransmitting, by a transmitter, the exact zero tail data signal.

According to another embodiment, a wireless communication deviceconfigured to transmit an exact zero tail data signal in wirelesscommunications is provided. The wireless communication device includesat least one processor configured to generate a data signal by mapping,in a frequency domain, a plurality of data symbols and a plurality ofzeros to a plurality of allocated subcarriers in an interleaved mannersuch that the plurality of zeros are mapped to empty subcarriers of theplurality of allocated subcarriers interleaved among data subcarriers ofthe plurality of allocated subcarriers; the at least one processor isfurther configured to convert the data signal to a time-domain andselect a plurality of tail time-domain samples from a tail portion ofthe converted data signal; the at least one processor is furtherconfigured to generate a cancellation signal from the selected pluralityof tail time-domain samples; the at least one processor is furtherconfigured to generate the exact zero tail data signal in the timedomain by combining the cancellation signal with the converted datasignal such that the tail portion of the data signal is canceled; and atransmitter configured to transmit the exact zero tail data signal.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 illustrates an example of a millimeter wave (mmW) small celldeployment system according to one or more embodiments;

FIG. 3 illustrates a comparison of frequency and spatial filtering;

FIG. 4 illustrates an exemplary orthogonal frequency divisionmultiplexing (OFDM) frame structure;

FIG. 5 is diagram which illustrates a channel mapping of mmW downlinklogical, transport and physical channels;

FIG. 6 illustrates millimeter wave WTRU (mWTRU) fully digitizedbeamforming;

FIG. 7 illustrates mWTRU analog beamforming with one PAA and one RFchain;

FIG. 8 illustrates mWTRU analog beamforming with one PAA and two RFchains;

FIG. 9 illustrates mWTRU analog beamforming with two PAAs and two RFchains;

FIG. 10 illustrates mWTRU analog beamforming with two PAAs and one RFchain;

FIG. 11A illustrates a two dimensional (2D) narrow beam pattern;

FIG. 11B illustrates a three dimensional (3D) narrow beam pattern;

FIG. 12 illustrates a 3D broadside broad beam pattern;

FIG. 13 is a block diagram which illustrates a zero tail (ZT) discreteFourier transform (DFT) spread OFDM (DFT-s-OFDM) transmitter accordingto one or more embodiments;

FIG. 14 illustrates a block diagram zero tail/head generation accordingto one or more embodiments;

FIG. 15 is a block diagram of an exemplary unique word (UW) OFDMtransmitter according to one or more embodiments;

FIG. 16 is an flow diagram which illustrates an iterative approachimplemented in a transmitter for exact zero tail generation for discreteFourier transform spread (DFT-s) according to one or more embodiments;

FIG. 17 illustrates a block diagram of a guard band insertion blockimplemented in a frequency domain according to one or more embodiments;

FIG. 18 illustrates a block diagram of a guard band insertion blockimplemented in a time domain according to one or more embodiments;

FIG. 19 is a block diagram of a transmitter utilizing time-domain tailcancellation prior to guard band insertion according to one or moreembodiments;

FIG. 20 is a block diagram of a transmitter utilizing UW support usingeZT DFT-s OFDM according to one or more embodiments;

FIG. 21 illustrates a block diagram of a multi-user transmitterutilizing exact zero tail (eZT) DFT-s OFDM according to one or moreembodiments;

FIG. 22 is a block diagram of a transmitter utilizing tail cancellationin time domain after guard band insertion according to one or moreembodiments;

FIG. 23 is a block diagram of a receiver according to one or moreembodiments;

FIG. 24 illustrates bit error rate (BER) performance of eZT DFT-s and ZTDFT-s embodiments in high delay spread channels according to one or moreembodiments;

FIG. 25 illustrates peak to average power ratio (PAPR) of eZT DFT-s ODFMcompared to ZT DFT-s OFDM according to one or more embodiments;

FIG. 26 illustrates out of band (OOB) emissions of eZT DFT-s OFDMcompared to cyclic prefix (CP) and ZT DFT-s OFDM according to one ormore embodiments;

FIG. 27 is time-domain illustration of the tail for eZT DFT-s comparedto ZT DFT-s according to one or more embodiments;

FIG. 28 illustrates multi-user versus single user performance for eZTDFT-s OFDM according to one or more embodiments;

FIG. 29 is a flow diagram which illustrates an iterative approachimplemented in a transmitter for exact zero tail generation for OFDMaccording to one or more embodiments;

FIG. 30 illustrates a block diagram of a guard band insertion blockimplemented in a frequency domain according to one or more embodiments;

FIG. 31 illustrates a block diagram of a guard band insertion blockimplemented in a time domain according to one or more embodiments;

FIG. 32 is a block diagram of a transmitter utilizing a time-domain tailcancellation for OFDM according to one or more embodiments;

FIG. 33 illustrates data signal with UW insertion according to one ormore embodiments;

FIG. 34 is a block diagram of a transmitter utilizing UW support for eZTOFDM according to one or more embodiments;

FIG. 35 is a block diagram of a guard band insertion block for eZT OFDMaccording to one or more embodiments;

FIG. 36 illustrates a block diagram of a transmitter tail cancellationand UW insertion for OFDM according to one or more embodiments;

FIG. 37 illustrates a block diagram of a transmitter for multi-user eZTOFDM according to one or more embodiments;

FIG. 38 illustrates a block diagram a transmitter for multi-user eZTOFDM according to one or more embodiments;

FIG. 39 illustrates BER simulation results for eZT OFDM according to oneor more embodiments;

FIG. 40 illustrates out-of-band emission of eZT-OFDM according to one ormore embodiments;

FIG. 41 illustrates selective addition of UW in both eZT-DFT-s-OFDM andeZT-OFDM achieved in the time domain according to one or moreembodiments; and

FIG. 42 illustrates a block diagram of a transmitter for DFT-s-OFDM withzero head generation according to one or more embodiments.

DETAILED DESCRIPTION

In the following, a plurality of details are set forth to provide a morethorough explanation of the exemplary embodiments. However, it will beapparent to those skilled in the art that embodiments may be practicedwithout these specific details. In other instances, well-knownstructures and devices are shown in block diagram form or in a schematicview rather than in detail in order to avoid obscuring the embodiments.In addition, features of the different embodiments described hereinaftermay be combined with each other, unless specifically noted otherwise.

Embodiments described herein may define transmission modes (includingreference signals and channel state information (CSI) feedback) andtransmission schemes for operation of highly directional beamformedsystems. In addition, embodiments may define how to mitigate controland/or data channel performance loss due to narrow beam misalignment,for example, for systems operating in higher frequency bands (e.g.,above-6 GHz frequencies).

The latter problem can further be broken down into two differentscenarios. In the first scenario, a change in the wirelesstransmit/receive unit (WTRU) orientation may be such that the datachannel performance using a narrow beam pair may be significantlydegraded, while the downlink (DL) wide beam control channel may still bereceived by the WTRU. In the second scenario, the WTRU orientationchange may be such that both the data and the control channels may notbe received by the WTRU.

Embodiments may include downlink/uplink (DL/UL) transmission schemes forthe access link of beamformed systems operating in the high frequencybands (e.g., above 6 GHz) using one or multiple radio frequency (RF)chains. In addition embodiments may define DL/UL transmission modes andmodes of operations.

In addition to presenting transmission schemes and transmission modesfor above 6 GHz systems, embodiments described herein that areapplicable to systems operating below 6 GHz and may include variousscenarios where significant degradation of the control and/or datachannel performance may occur due to transmit-receive (Tx-Rx) beammisalignment. Embodiments may address techniques for control and datafallback to maintain connectivity until a transmission mode change or abeam change is performed. Thus, embodiments may provide solutions thatleverage the bandwidths available both below-6 GHz and above-6 GHzfrequencies.

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNode B,a Home Node B, a Home eNode B, a site controller, an access point (AP),a wireless router, and the like. While the base stations 114 a, 114 bare each depicted as a single element, it will be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessembodiments, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

One or more of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive radio frequency (RF) signals. In another embodiment, thetransmit/receive element 122 may be an emitter/detector configured totransmit and/or receive IR, UV, or visible light signals, for example.In yet another embodiment, the transmit/receive element 122 may beconfigured to transmit and receive both RF and light signals. It will beappreciated that the transmit/receive element 122 may be configured totransmit and/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managemententity gateway (MME) 142, a serving gateway 144, and a packet datanetwork (PDN) gateway 146. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MME 142 may be connected to each of the eNode-Bs 140 a, 140 b, 140 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

Other network 112 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 160. The WLAN 160 may include anaccess router 165. The access router may contain gateway functionality.The access router 165 may be in communication with a plurality of accesspoints (APs) 170 a, 170 b. The communication between access router 165and APs 170 a, 170 b may be via wired Ethernet (IEEE 802.3 standards),or any type of wireless communication protocol. AP 170 a is in wirelesscommunication over an air interface with WTRU 102 d.

It should be noted that although 3GPP LTE may be used for examplepurposes, the techniques described herein may be applied to any othersystem.

The following list of definitions, although not intended to be limiting,may be helpful in understanding the following embodiments.

A “beam” may be one of the lobes, for example, main/side/grating lobesof the transmit radiation pattern and receive gain pattern of an antennaarray. A beam may also denote a spatial direction that may berepresented with a set beamforming weights. A beam may be identified orassociated with a reference signal, an antenna port, a beam identity(ID), and/or a scrambling sequence number. A beam may be transmittedand/or received at a specific time, frequency, code, and/or spatialresource. A beam may be formed digitally, in an analog manner, or both(i.e., hybrid beamforming). The analog beamforming may be based on fixedcode-book or continuous phase shifting.

A “beam-specific reference signal” (BSRS) may be a sequence associatedwith a transmit beam used for beam acquisition, timing and/or frequencysynchronization, channel estimation for a physical downlink directionalcontrol channel (PDDCCH), fine beam tracking, beam measurement, etc.BSRS may carry (e.g., implicitly carry) beam identity information. Theremay be different types of BSRS. For example, there may be BSRS for anmmW sector and its member segments. The segment may be referred as abeam direction (e.g., a narrow beam direction or a wide beam direction).

A “data channel beam” may be used to transmit a data channel, a PhysicalDownlink Shared Channel (PDSCH), a mPDSCH, a mmW PDSCH, a mmW datachannel, a directional PDSCH, a beamformed data channel, a spatial datachannel, a data channel slice, or a high frequency data channel. Thedata channel beam may be identified or associated with a referencesignal, an antenna port, a beam identity (ID), and/or a scramblingsequence number. The data channel beam may be transmitted and/orreceived at a specific time using frequency, code, and/or spatialresources.

A “control channel beam” may be used to transmit a control channel, acontrol channel beam, a PDCCH, an mPDCCH, an mmW PDCCH, an mmW controlchannel, a directional PDCCH, a beamformed control channel, a spatialcontrol channel, a control channel slice or a high frequency controlchannel. A control channel beam may be identified or associated with areference signal, an antenna port, a beam identity (ID), a scramblingsequence number and may be transmitted and/or received at a specifictime and/or frequency and/or code and/or spatial resources.

A “measurement beam” may be used to transmit a signal or channel forbeam measurement. This may include a beam reference signal, a beammeasurement reference signal, Cell Specific Reference Signal (CRS),Channel State Information-Reference Signal (CSI-RS), CSI-interferencemeasurement (CSI-IM), etc. The measurement beam may be identified orassociated with a reference signal, an antenna port, a beam identity(ID), and/or a scrambling sequence number. The measurement beam may betransmitted and/or received at a specific time, frequency, code, and/orspatial resource.

A “control channel beam duration” may be the length in the time domain,which may be referred to in units of OFDM symbols, used within ascheduling interval for the transmission of one control channel beam.For example, a control channel beam duration may be a number of OFDMsymbols in a TTI occupied by one control channel beam.

A “control region” may be the length in the time domain, which may bereferred to in units of OFDM symbols, used within a scheduling intervalfor the transmission of all the control channel beams in that schedulinginterval. For example, a control region may be the number of OFDMsymbols in a TTI occupied by all the control channel beams transmittedin the TTI.

A “data region” may be part of the scheduling interval in time domain,which may be referred to in units of OFDM symbols, used for thetransmission of all data channel beams in that scheduling interval.

In one or more embodiments described herein, the terms base station,eNode-B (eNB), mmW eNB (mB), Small Cell mmW eNB (SCmB), cell, smallcell, primary cell (Pcell), and secondary cell (Scell) may be usedinterchangeably. In some embodiments, the term operate may be usedinterchangeably with transmit and/or receive. In some embodiments, theterms component carrier, mmW carrier may be used interchangeably withserving cell.

In one or more embodiments, the mB may transmit and/or receive one ormore mmW channels and/or signals in a licensed band and/or an unlicensedband.

In some embodiments, the term WTRU may be substituted for eNB and/orvice versa and still be consistent with this disclosure. In someembodiments, UL may be substituted for DL and/or vice versa and still beconsistent with this disclosure.

In one or more embodiments, a channel may refer to a frequency band thatmay have a center frequency (i.e., a carrier frequency) and a bandwidth.Licensed and/or unlicensed spectrum may include one or more channelswhich may or may not overlap. Channel, frequency channel, wirelesschannel, and mmW channel may be used interchangeably. Accessing achannel may be the same as using (e.g., transmitting and/or receiving onor using) a channel.

In one or more embodiments, a channel may refer to a mmW channel orsignal, such as an uplink or downlink physical channel or signal.Downlink channels and signals may include one or more of the following:mmW synchronization signal, mmW broadcast channel, mmW cell referencesignal, mmW beam reference signal, mmW beam control channel, mmW beamdata channel, mmW hybrid automatic repeat request (ARQ) indicatorchannel, mmW demodulation reference signal, primary synchronizationsignal (PSS), secondary synchronization signal (SSS), demodulationreference signal (DMRS), CRS, CSI-RS, Physical Broadcast Channel (PBCH),Physical downlink Control Channel (PDCCH), Physical Hybrid ARQ IndicatorChannel (PHICH), Enhanced Physical Downlink Control Channel (EPDCCH),and PDSCH. Uplink channels and signals may include one or more of thefollowing: mmW Physical Random Access Channel (PRACH), mmW controlchannel, mmW data channel, mmW beam reference signal, mmW demodulationreference signal, PRACH, Physical Uplink Control Channel (PUCCH),sounding reference signal (SRS), DMRS and Physical Uplink Shared Channel(PUSCH). Channel and mmW channel may be used interchangeably. Channelsand signals may be used interchangeably. PRACH and preamble may also beused interchangeably.

In one or more embodiments, data may mean data signal and/or datachannel, and control may mean control signal and/or control channel.Control may include synchronization. The data/control may be mmWdata/control. Data/control, data/control channels, and/or data/controlsignals may be used interchangeably. The terms control channel, controlchannel beam, PDCCH, mPDCCH, mmW PDCCH, mmW control channel, directionalPDCCH, beamformed control channel, spatial control channel, controlchannel slice, high frequency control channel may be usedinterchangeably. The terms data channel, data channel beam, PDSCH,mPDSCH, mmW PDSCH, mmW data channel, directional PDSCH, beamformed datachannel, spatial data channel, data channel slice, and high frequencydata channel may be used interchangeably.

In one or more embodiments, channel resources may be resources (e.g.,3GPP LTE or LTE-A resources) such as time, frequency, code, and/orspatial resources, which may, at least sometimes, carry one or morechannels and/or signals. In some embodiments, channel resources may beused interchangeably with channels and/or signals.

The terms mmW beam reference signal, mmW reference resource for beammeasurement, mmW measurement reference signal, mmW channel statemeasurement reference signal, mmW demodulation reference signal, mmWsounding reference signal, reference signal, CSI-RS, CRS, DM-RS, DRS,measurement reference signal, reference resource for measurement,CSI-IM, and measurement RS may be used interchangeably. mmW cell, mmWsmall cell, SCell, secondary cell, license-assisted cell, unlicensedcell, and Licensed Assisted Access (LAA) cell may be usedinterchangeably. The terms mmW cell, mmW small cell, PCell, primarycell, LTE cell, and licensed cell may be used interchangeably.

The terms interference and interference plus noise may be usedinterchangeably.

A WTRU may determine the uplink (UL) and/or downlink (DL) directions ofone or more subframes according to one or more received and/orconfigured frequency division duplex (FDD) and/or time division duplex(TDD) UL/DL configurations. UL/DL and UL-DL may be used interchangeably.

In one or more embodiments, the terms transmit power, power, antennaarray transmit power may be used interchangeably. Further, in one ormore embodiments, cmW and mmW may be used interchangeably.

mmW deployment is disclosed herein such that SCmB deployment may bebased on a 3rd Generation Partnership Project (3GPP) Release 12 (R12)small cell deployment. The mmW operation may be performed by two networknodes including a SCmB and a mmW WTRU (mWTRU).

An SCmB may be an LTE small cell eNB capable of operating an mmW airinterface in parallel with a LTE air interface in the downlink. An SCmBmay be equipped with advanced antenna configuration and beamformingtechnique and may simultaneously transmit LTE downlink channels in awide beam pattern and mmW channels in narrow beam patterns. In order tosupport mmW WTRUs without mmW uplink transmission, an SCmB may supportnew features and procedures in the LTE uplink operation.

An mWTRU may be a WTRU capable of operating both an LTE and mmW airinterface in parallel. An mWTRU may have two sets of antennas andaccompanied RF chains, one operating in the LTE band and the other inthe mmW frequency band. A mWTRU may also include two independentbaseband processing functions. The two baseband functions may possiblyshare certain hardware (HW) blocks if the mmW air interface bearssimilarity with the LTE system.

The add-on mmW channels may be an extension of the LTE carrieraggregation embodiment with a new carrier type in the mmW frequency bandthat may apply a different air interface. mmW channels may lendthemselves to opportunistic use for high-throughput and/or low-latencytraffic data application.

Control signaling, for example, including system information update,paging, radio resource control (RRC) and network access stratum (NAS)signaling (signaling radio bearers) and multicast traffic may be carriedin LTE channels. In addition, certain mmW L1 control signaling may becarried in LTE channels.

Due to the high propagation loss, especially in non-line of sight (NLOS)environments at a mmW frequency band, one or both of an SCmB and mWTRUmay employ narrow beamforming, for example to ensure sufficient linkbudget for high-throughput and low-latency data transmission.

Transmit and receive narrow beam pairing may be critical in certainscenarios. For example, at 28 GHz and 38 GHz in urban area usingsteerable 10°-beamwidth and 24.5-dBi horn antenna at both transmitterand receiver, a consistent coverage with a cell-radius of up to 200meters may be achieved.

As indicated above, systems operating at high carrier frequency (e.g.,above 6 GHz) may need to use beamforming (analog, digital or hybrid) tocompensate for a 20-30 dB pathloss since it becomes more significant asthe carrier frequency becomes higher. The beamforming may be used at thetransmitter and/or at the receiver. The highest beamforming may beachieved when both transmitter and receiver use beamforming and the beamdirections are aligned (e.g., transmitter and receiver beams arepaired). The transmit and receive beam widths may be determined as afunction of the type, size and number of antenna elements of the phasedarray antenna (PAA).

FIG. 2 illustrates an example of an SCmB deployment system 200. Inaddition to a downlink transmit narrow beam and a downlink receivenarrow beam used by the SCmB and the mWTRUs, respectively, a broad beampattern (wide beam) may also be applied for LTE operations includingcell search, random access, cell selection/reselection, etc. Forexample, as shown in FIG. 2, a first mWTRU 202 and a second mWTRU 204communicate with a SCmB 206. The SCmB may use a downlink wide transmitbeam 210 and downlink narrow transmit beams 212 a and 212 b fortransmitting signals to one or more of the mWTRUS 202 and 204. The firstmWTRU 202 and the second mWTRU 204 may use downlink wide beams 214 and215, respectively, for receiving signals transmitted by the SCmB usingthe wide transmit beam 210. In addition, first mWTRU 202 and the secondmWTRU 204 may use downlink narrow beams 216 a and 216 b, respectively,that reside in the wide transmit beam 210 and are used for receivingsignals transmitted by the SCmB using the narrow transmit beams 212 aand 212 b, respectively. When a downlink receive narrow beam (e.g., 216a or 216 b) is aligned with downlink transmit narrow beam (e.g., 212 aand 212 b), the receive and transmit narrow beams are referred to as“paired” and form a Tx-Rx beam pair.

FIG. 3 illustrates a comparison of frequency (top) and spatial filtering(bottom). The mWTRU receive beam forming may be regarded as narrowspatial filtering as shown in FIG. 3. To better demonstrate the effectof spatial or angular filtering, a comparison with a frequency domainfiltering is also shown in FIG. 3.

In a similar approach to how frequency filtering removes unwantedfrequency components, spatial filtering may allow a mWTRU to detect achannel impulse response at a distinct angular direction captured by thenarrow receive beam. This may result in a flat effective channel byexcluding angular incoming paths outside of its beamwidth. An LTE WTRUmay be assumed to have an omni-directional receive beam pattern andconsequently may perceive a superimposed channel impulse response overthe entire angular domain. Therefore, an aligned mmW transmit andreceive beam pair may provide an additional degree of freedom in theangular domain as compared with current LTE systems.

Accordingly, a mmW system, for example, a downlink system design mayfocus on integrating directivity (e.g., the directivity of a narrowtransmit and receive beam pair) into cellular system procedures whichmay include physical layer 1 (L1) control signaling, data scheduling,narrow beam pairing, beam measurement, L1 control information feedback,etc.

Exemplary mmW system parameters and assumptions are disclosed herein.These parameters and assumptions may change. These parameters andassumptions are not intended to be limiting but serve to illustrate onepossible set of parameters and assumptions of an example mmW system.

A carrier frequency may be 28 GHz. This is intended for exemplary systemnumerology, but embodiments disclosed herein may be extended to othermmW frequencies such as 38 GHz, 60 GHz, 72 GHz, etc. A system bandwidthmay be variable up to 1 GHz with aggregation to a higher bandwidth. Anestimated root mean square (RMS) delay spread may be 100-200 ns with anarrow beam pattern. A required latency may be 1 millisecond (ms). Awaveform may be OFDM-based or broad-band-single-carrier-based.Connectivity may be available using an LTE Small Cell eNB with mmWadd-on channels and two separate antennas and RF chains connected to twodifferent antenna solutions. Exemplary data rates may achieve a DLminimum 30 megabit (Mbit)/s for at least 95% of mWTRUs. Mobility may beoptimized data for a data connection at 3 km/h and maintain a connectionat 30 km/h. Coverage may meet the data rate and mobility requirementwith less than a 100-m cell radius.

A frame structure for the system may depend on the applied waveform. Atransmission time interval (TTI) length such as 100 us may be used, forexample to achieve low latency. A system bandwidth such as one in therange of 50 MHz to 2 GHz may be used, for example, to achieve high datarates.

In one or more embodiments, an OFDM frame structure may be utilized. AmmW frame structure of an OFDM-based waveform may offer flexibility incoordination between the LTE and mmW channels and possibly enable commonfunctional block sharing in a mWTRU device. An example is presentedherein.

A mmW sampling frequency may be selected as an integer multiple of theLTE minimum sampling frequency of 1.92 MHz, which may lead to an mmWOFDM sub-carrier spacing Δf being an integer multiple of the LTEsub-carrier spacing of 15 kHz, i.e. Δf=15*K kHz. The selection of theinteger multiple K and the resulting Δf may take into consideration thesensitivity to the Doppler shift, different types of frequency errorsand the ability to remove channel time dispersion. The orthogonalitybetween sub-carriers may deteriorate and inter-sub-carrier interference(ISI) may increase when the Doppler shift increases in proportion to thesub-carrier spacing.

For example, the maximum Doppler shift at 30 km/h and 28 GHz is 778 Hz.The latest 28-GHz channel time dispersion measurement in dense urbanarea by Poly New York University (NYU) indicates the RMS delay spread σis between 100 and 200 ns up to 200-m cell radius. The 90% coherencebandwidth may be estimated at 1/50σ of 100 kHz and the 50% coherencebandwidth at ⅕σ of 1 MHz ([15]).

A sub-carrier spacing Δf between 100 kHz and 1 MHz may thus bereasonable. A sub-carrier spacing of 300 kHz (K=20) may be robustagainst Doppler shift and other types of frequency error and reduceconsiderably the implementation complexity. The corresponding symbollength (1/Δf) is 3.33 us.

A cyclic prefix (CP) length is normally required to span over the entirelength of the channel time dispersion in order to eliminate theinter-symbol-interference. On the other hand, as a cyclic prefix (CP)does not carry useful data, a long CP may cause excessive systemoverhead. One example of CP length for a T_(symbol) of 3.33 us may beselected at 1/14 of T_(symbol), 0.24 us and the corresponding CPoverhead is 7% as calculated by T_(CP)/(T_(CP)+T_(symbol)).

In order to achieve low latency, the TTI length of the mmW transmissionmay be reduced significantly compared to the 1-ms TTI length of the LTEsystem. It may be beneficial to have a mmW sub-frame length of 1 ms toalign with the LTE 1-ms sub-frame timing. Though the mmW sub-frame maycontain multiple mmW TTIs whose length is tied to other parameters suchas sub-carrier spacing, symbol length, CP length, FFT size, etc.

With all consideration taken into account, an example with aconservative CP length using a 4× channel delay spread is summarized inTable 1. It should be noted the CP length selection is based on theassumption that the delay spread over all potential mmW frequency bandsis lower than 200 ns.

TABLE 1 Exemplary mmW Downlink OFDM Numerology OFDM NumerologyParameters System bandwidth (MHz) 125 250 500 1000 Sampling rate (MHz)153.6 307.2 614.4 1228.8 Sub-carrier spacing (kHz) 300 300 300 300Number of sub-carrier per RB 12 12 12 12 RB bandwidth (MHz) 3.6 3.6 3.63.6 Number of assignable RBs 32 64 128 256 Number of occupiedsub-carriers 384 768 1536 3072 Occupied bandwidth (MHz) 115.2 230.4460.8 921.6 IDFT(Tx)/DFT(Rx) size 512 1024 2048 4096 OFDM symbolduration (us) 3.333 3.333 3.333 3.333 CP length (ratio to symbol 1/4 1/41/4 1/4 length) CP length (us) 0.833 0.833 0.833 0.833 Number of symbolsper slot 24 24 24 24 Slot duration (TTI) (us) 100 100 100 100 Sub-frameduration (ms) 1 1 1 1 Number of slots per sub-frame 10 10 10 10 Frameduration (ms) 10 10 10 10 Number of sub-frames per frame 10 10 10 10Number of symbols per TTI per 288 288 288 288 RB Number of symbols perTTI 9216 18432 36864 73728 using all RBs Signaling overhead 20% 20% 20%20% Data rate using uncoded 64 442.368 884.736 1769.472 3538.944 QAM(Mbps) Spectral efficiency 3.538944 3.538944 3.538944 3.538944

FIG. 4 depicts an example OFDM-based frame structure. In the example,the system bandwidth is 1 GHz and a sub-carrier spacing of 300 kHz witha corresponding symbol length of 3.33 μs is used. An example CP lengthof ¼ of T_(symbol) which equals 0.833 μs is used. Accordingly, FIG. 4shows a diagram of an OFDM frame structure 400 over a 1-GHz systembandwidth. According to the OFDM-based frame structure 400 shown in FIG.4, a frame 402 includes 10 sub-frames, each sub-frame includes 10 slots,and each slot includes 24 symbols. The OFDM-based frame structure 400may have, for example, a sub-carrier spacing of 300 kHz with acorresponding symbol length (T_(symbol)) of 3.33 μs. Considering a CPlength may span over the entire length of the channel time dispersion inorder to eliminate the inter-symbol-interference, one example of CP fora T_(symbol) of 3.33 μs may be selected at ¼ of T_(symbol) (i.e., at0.833 μs). This example numerology may be used for a range of above-6GHz system bandwidths (e.g., from 50 MHz to 2 GHz) with correspondingFast Fourier Transform (FFT) length.

The frame structure and example disclosed herein assumes an OFDM-basedmmW waveform, which may be readily incorporated into the OFDM-based LTEsmall cell network. However, the system procedure design disclosed inthe subsequent sections is not bound by this specific frame structureand may be applied to other waveform candidates.

Exemplary mmW physical channels are disclosed herein. An SCmB deploymentmay employ new mmW physical layer channels and reference signals asdescribed herein in addition to the existing LTE physical channels.

A beam-specific reference signal (BSRS) may be a unique sequencetransmitted per transmit beam used for beam acquisition,timing/frequency synchronization, channel estimation for a physicaldownlink directional control channel (PDDCCH), beam tracking andmeasurement, etc. It may implicitly carry beam identity informationincluding a BSRS sequence index. It should be noted that there may bedifferent types of BSRS. A BSRS resource allocation may be pre-defined.

An adaptive antenna reference signal (AARS) may be a unique sequencescheduled and transmitted dynamically for the purpose of beam pairmeasurement specific to one antenna port. It may embed implicitly thebeam identity information in the sequence index or carry a small payloadincluding the same information.

A physical downlink directional data channel (PDDDCH) may carry all datarelated control information for a mWTRU to identify, demodulate anddecode the associated PDDDCH correctly. The PDDCCH may be carried in ammW narrow beam or broad beam and may apply different multiple access.

For example, there may be a common PDDCCH transmitted in downlink mmWbroad beam covering a sector or cell and a dedicated PDDCCH onlytransmitted in a narrow beam pair when mWTRU-specific data transmissionis on-going. The dedicated PDDCCH may carry scheduling information forits associated PDDDCH on a per-TTI basis and may not carry beam specificinformation. A common PDDCCH may include cell-specific informationincluding sector/segment identity or beam identity. In addition, a mWTRUmay read the common PDDCCH to determine if it is scheduled for narrowbeam pairing procedure in order to begin narrow beam data transmissionsubsequently.

A PDDDCH may carry payload information received in the form of a MAC PDUfrom mmW MAC layer. The complete resource allocation of this channel isdetermined by the downlink scheduling information carried in PDDCCH. ThePDDDCH intended for a mWTRU may be transmitted in a transmit (Tx) narrowbeam and received in a properly paired receive (Rx) narrow beam, forexample a narrow beam pair. Due to this spatial isolation, PDDDCHs fordifferent WTRUs in different beam pairs may reuse a time, frequency, orcode resource. Multiple PDDDCHs may also operate in one beam pair usingmultiple access in a time, frequency, or code domain. In addition, acommon PDDDCH may be used to carry data in broad mmW antenna patternassociated with the common PDDCCH.

A demodulation reference signal (DMRS) may include symbols embedded inthe transmission for channel estimation for PDDDCH. They are placed inboth the time and frequency domain according to a pre-defined pattern toensure correct interpolation and reconstruction of the channel.

Channels and reference signals in a narrow beam pair are beamformedidentically and considered to be transmitted via one physical antennaport. Given the directivity of the transmission of these channels,carrying broadcast or multicast information may not be an optimalapplication. Accordingly, the SCmB deployment with mmW downlink datatransmission may adopt a channel mapping as illustrated in FIG. 5 withmmW channels. Specifically, FIG. 5 is diagram which illustrates achannel mapping of mmW downlink logical, transport and physical channelswith the mmW channels shown with shading. The mapping shows the variouschannels connected to Multimedia Broadcast Multicast Service(MBMS)/Multicast-broadcast single-frequency network (MBSFN) single-cell500 having multiplexing and hybrid automatic repeat request (HARQ)control functionality.

The downlink logical channels include: a PCCH—Paging Control Channel, aBCCH—Broadcast Control Channel, a CCCH—Common Control Channel, aDCCH—Dedicated Control Channel, a DTCH—Dedicated Traffic Channel, anMCCH—Multicast Control Channel, and an MDCH—Multicast Data Channel.

The downlink transport channels include: a PCH—Paging Channel, aBCH—Broadcast Channel, a DL-SCH—Downlink Shared Channel, anMCH—Multicast Channel, and a DL-DDCH—Downlink Directional Data Channel.

The downlink physical channels include: a PBCH—Physical BroadcastChannel, a PDSCH—Physical Downlink Shared Channel, a PMCH—PhysicalMulticast Channel, a PDDDCH—Physical Downlink Directional Data Channel,a PDCCH—Physical Downlink Control Channel, an EPDCCH—Enhanced PhysicalControl Channel, a PHICH—Physical HARQ Indicator Channel,PCFICH—Physical Control Format Indicator Channel, and a PDDCCH—PhysicalDownlink Directional Control Channel.

A mWTRU may use a phase antenna array to achieve the beamforming gainnecessary to compensate the high path loss at mmW frequencies, at whichthe short wavelength allows a compact form factor of the device design.While an element spacing of 0.5λ is typically used in theoreticalperformance analysis, in practice a large spacing such as 0.7λ may beapplied.

Referring now to FIG. 6, FIG. 6 shows a diagram illustrating a fullydigitized beamforming system 600 according to one or more embodiments. Aphase antenna array (PAA) may be used for beamforming with elementspacing, e.g., at 0.5λ. The phase antenna may apply differentbeamforming algorithms. A fully digitized beamforming approach may havea dedicated RF chain including an RF processor 601 and ananalog-to-digital converter (ADC) 602 for each antenna element 603. Thesignal 604 processed by each antenna element 603 may be controlledindependently in phase and amplitude to optimize the channel capacity. Abaseband (BB) processor 605 is configured to perform BB processing oneach dedicated RF chain based on the signals received from each ADC 602.

Thus, the configuration shown in FIG. 6 has the same number of RF chainsand ADCs as that of antenna elements. While offering very highperformance, this mWTRU antenna configuration may impose a very highcost and complexity in implementation and cause high energy consumptionin operation. Thus, the fully digitized beamforming may not be adoptedin the initial roll-out of mWTRU implementation and could becomefeasible in the future with advanced technology.

Referring now to FIG. 7, FIG. 7 shows a diagram illustrating an analogbeamforming system 700 according to one or more embodiments. In thisembodiment, the analog beamforming may be with one PAA and one RF chain.The analog beamforming may apply one RF chain for a number of antennaelements 703 that process the signal 704. Each antenna element 703 maybe connected to a phase shifter 706 that may be used to set the weightfor beamforming and steering. The RF chain further includes an RFprocessor 701 and an ADC 702 which provides an output to a BB processor705. The implemented number of RF chains may be significantly reduced aswell as the energy consumption.

It should be noted that in this case only the phase of the signal ateach antenna element is adjusted in the beamforming. The phase shiftingand combining may be implemented in different stages (e.g., at RF state,at BB analog stage, or at Local Oscillator (LO) stage). One example is asingle-beam analog configuration. It may operate one beam at a time andthe single beam may be placed at, for example, the strongest angulardirection such as a line of sight (LOS) path obtained from beammeasurement. A broad beam pattern may cover a range of angulardirections at the expense of reduced beamforming gain. Furthermore, eachexemplary solution may be evaluated in terms of signal loss, phaseerror, power consumption, etc.

The mWTRU analog beamforming algorithms may include fixed codebook-basedbeamforming and continuous phase shifting beamforming.

For example, using fixed codebook-based beamforming, a grid of beams arecomprised of a set of fixed beams. Each beam is formed by the mWTRUapplying a beamforming weight vector v chosen from a pre-definedcodebook v ∈{v₁, v₂, v₃ . . . V_(N)} where N denotes the number of fixedbeams. Each vector may include pre-calibrated phase shifts for all phaseshifters and thus represent a unique analog beam direction, i.e.,“beam.” The number of beams may depend on the Half-Power-Beam-Width(HPBW) of the beamforming and desired coverage.

Using continuous phase shifting beamforming, the desired weight of eachphase shifter may be calculated based on the estimated short-termchannel information and converted using a high resolutiondigital-to-analog converter (DAC) in order to apply to the phaseshifter. Continuous phase shifting beamforming may provide a continuousand adaptive beamforming to track the channel conditions. The algorithmmay perform well in scenarios with increased multipath, high angularspread and low WTRU mobility.

Combining both the digitized and analog beamforming, a mWTRU may employa hybrid approach. This approach may include analog beamformingperformed over the phase array antenna elements each associated with aphase shifter and all connected to one RF chain. This approach mayfurther include digital precoding applied on the baseband signal of eachRF chain when there is more than one RF chain. MIMO embodiments may beimplemented using digital precoding.

The basic system parameters of hybrid beamforming may include a numberof data streams (NDATA), a number of RF chains TRX (NTRX), a number ofantenna ports (NAP), a number of antenna elements (NAE), and a number ofphase antenna arrays (NPAA). The configuration of these parameters mayimpact on the system function and performance as disclosed herein. Inone or more embodiments, the parameters may be configured as follows:N_(PAA)≤N_(AP)≤N_(TRX)≤N_(AE).

One PAA may be comprised of multiple antenna elements, for example a PAAof size 4×4 has 16 antenna elements. An antenna port may be defined suchthat the channel over which a symbol on the antenna port is conveyed maybe inferred from the channel over which another symbol on the sameantenna port is conveyed. There is one resource grid per antenna port.For reference purposes, the LTE R12 antenna port configurations arelisted herein. Cell-specific reference signals may support aconfiguration of one, two, or four antenna ports and are transmitted onantenna ports p=0, p ∈{0,1} and p ∈{0,1,2,3}, respectively. MBSFNreference signals are transmitted on antenna port p=4. WTRU-specificreference signals associated with PDSCH are transmitted on antennaport(s) p=5, p=7, p=8, or one or several of p ∈{7,8,9,10,11,12,13,14}.Demodulation reference signals associated with EPDCCH are transmitted onone or several of p ∈{107,108,109,110}. Positioning reference signalsare transmitted on antenna port p=6. CSI reference signals support aconfiguration of one, two, four or eight antenna ports and aretransmitted on antenna ports p=15, p ∈{15,16}, p ∈{15,16,17,18}, and p∈{15,16,17,18,19,20,21,22}, respectively. Each antenna port may carry abeamformed reference signal uniquely associated with this antenna portthat may be used to identify the antenna port. When the number of RFchains (N_(TRX)) equals the number of antenna elements (N_(AE)), forexample, one RF chain per antenna element, the antenna configurationbecomes fully digitized solution as shown in FIG. 6.

One PAA may be connected to one RF chain, as shown in FIG. 7, ormultiple RF chains depending on the system requirement andconfiguration, as shown in FIG. 8. FIG. 8 illustrates an mWTRU analogbeamforming system 800 with one PAA and two RF chains. One antenna portmay carry a beamformed reference signal uniquely associated with thisantenna port that may be used to identify the antenna port. One PAA maybe connected to one RF chain or multiple RF chains depending on thesystem requirement and configuration. In FIG. 8, one PAA of size 4×4with 16 antenna elements 803, for receiving a signal 804, may beconnected to two RF chains and each RF chain may have a set of 16 phaseshifters 806 a and 806 b. The PAA may form two narrow beam patternswithin a +45° and −45° coverage in an azimuth plane. In thisconfiguration, N_(PAA)<N_(AP)=N_(TRX)<N_(AE). Each RF chain furtherincludes an RF processor 801 a or 801 b and an ADC 802 a or 802 b whichprovide an output to a BB processor 805.

FIG. 9 shows a another example where there are two PAAs and each PAA hasa dedicated RF chain, for example, N_(PAA)=N_(AP)=N_(TRX)≤N_(AE). Inparticular, FIG. 9 shows a diagram illustrating analog beamformingsystem 900 with two PAAs and two RF chains. Each PAA may have a set ofantenna elements 903 a and 903 b, respectively, for receiving signals904 a and 904 b. Each antenna element 903 a, 903 b may be connected to aphase shifter 906 a, 906 b, respectively. Each dedicated RF chain mayinclude an RF processor 901 a, 901 b and an ADC 902 a, 902 b whichprovide an output to a BB processor 905. This configuration may allowspatial independence between the two simultaneous signals 904 a and 904b by placing the PAAs at different orientations (e.g., in an azimuthplane). An aligned PAA arrangement may provide an aggregated largercoverage compared to the configuration in FIG. 8. Both configurationswith two RF chains may apply Multiple Input Multiple Output (MIMO) withtwo data streams.

Referring now to FIG. 10, FIG. 10 shows a diagram illustrating analogbeamforming system 1000 with two PAAs having a set of antenna elements1003 a and 1003 b, respectively, for receiving signals 1004 a and 1004b. Thus, in this configuration, N _(AE)>N_(PAA)>N_(AP)=N_(TRX). Eachantenna element 1003 a, 1003 b may be connected to a phase shifter 1006a, 1006 b, respectively. The PAAs are connected to a single RF chainthat includes a switch 1008, an RF processor 1001 and an ADC 1002 thatprovides an output to a BB processor 1005. Multiple PAAs may beconnected to a single RF chain by using the switch 1008 (i.e.,N_(AE)>N_(PAA)>N_(AP)=N_(TRX)). Each PAA may form a narrow beam patterncovering from +45° to −45° in an azimuth plane. They may be orientedseparately so a single-beam network node may have a good coverage byusing a beam at different direction at different time instances.

According to another embodiment, the system parameters may be configuredas follows: N_(DATA)≤N_(TRX)≤N_(AE). Thus, when N_(DATA)=N_(TRX)=1, amWTRU has a single-beam configuration and may operate one beam at atime. The mWTRU beamforming under this configuration may form a narrowbeam pattern such as the one shown in FIGS. 11A and 11B for a 16×16 PAAat the strongest angular direction. Specifically, FIGS. 11A and 11Billustrate two dimensional (2D) narrow beam pattern and a threedimensional (3D) narrow beam pattern showing a LOS path obtained frombeam measurement. Here, a narrow beam forms in the strongest angulardirection.

FIG. 12 illustrates a 3D broadside broad beam pattern. The mWTRU mayform a broad beam pattern, for example, a wide main lobe such as the oneshown in FIG. 12 to cover a range of continuous angular directionsincluding both strong and weak ones in-between. However, it is notedthat the antenna gain may be reduced considerably with a broad beampattern and the link budget may worsen.

When N_(DATA)=1<N_(TRX), for example, when N_(TRX)=2, a mWTRU may havetwo simultaneous receive beam patterns, and the receive beam patternsmay be different and may also be used for different applications. ThemWTRU may place two narrow receive beam patterns at different angularincoming directions to receive one data stream. For example, coherentbeam combining may be used to utilize the spatial diversity and mitigatethe blockage effect and/or weak LOS condition. The mWTRU may form onenarrow receive beam and one broad receive beam for differentapplications. For example, the narrow receive beam may be used for datatransmission of a data channel and the broad receive beam may be usedfor control signaling of a control channel. When 1<N_(DATA)=N_(TRX), forexample, the transmitter may apply MIMO to increase the capacity in ahigh SNR channel condition. Furthermore, the mWTRU may place two narrowreceive beam patterns at different angular incoming directions toreceive two data streams in parallel.

Equivalently, the SCmB beam forming embodiments may also include fixedbeam, adaptive beam forming (e.g., codebook-based and non-codebook-basedbeam forming), and classical beam forming (e.g., direction-of-arrival(DoA) estimation). Each embodiment may require different procedures andwork well in certain scenarios. For example, the DoA estimation mayrequire a smaller angular spread and a mWTRU may need to transmit a LTEuplink reference signal to ensure DoA accuracy. The fixed beam system,on the other hand, may require beam cycling and switch procedures.

It should be noted that the mWTRU antenna configuration and beamformingdisclosed herein in the following exemplary embodiments are based on asingle-beam mWTRU antenna configuration with analog beamforming asillustrated in FIG. 7.

By way of background, the throughput of wireless communication systemshas increased significantly by new technologies introduced in LTE andWi-Fi. These technologies, however, are not sufficient to meet thedemands of future applications which will require Gbits/sec ofthroughput and latencies of 1 ms. Therefore, research on a new radioaccess technology, known as 5G, has already started.

One of the critical components of the 5G RAT will be the radio waveform.OFDM has been used for LTE and Wi-Fi due to its simplicity in convertinga frequency selective channel into smaller flat fading sub channels,allowing one-tap equalization per subchannel. Discrete Fourier Transform(DFT) spread OFDM (DFT-s-OFDM) improves the peak to average power ratio(PAPR) of OFDM by spreading the data sequence with DFT before loadingthe spread signal onto the subchannels.

Both OFDM and DFT-s-OFDM attach a cyclic prefix (CP) to prevent theinter-symbol interference (ISI) that may occur due to the channel delayspread, and to ensure cyclicity. The length of the CP is fixed anddimensioned for the maximum delay spread of the channel. This may resultin loss of spectral efficiency when the delay spread of the channel issmaller than the CP. The loss may be significant when the variance ofthe RMS delay spread of the channel is large. For example, in mmWchannels, the delay spread may be below 4 ns for indoor channels in LOSconditions, and up to 70 ns for indoor NLOS conditions. Since changingthe CP size would change the number of OFDM symbols in a subframe,configuring many different CP sizes is not feasible for a fixedsub-frame duration.

To address the limitation posed by the CP, several waveforms such aszero tail (ZT) Discrete Fourier Transform (DFT) spread OFDM (DFT-s-OFDM)and unique word (UW) OFDM are provided in the following embodiments.

Discrete Fourier Transform (DFT) spread OFDM (DFT-s-OFDM) is a singlecarrier (SC)-like transmission scheme that can be combined with OFDM andhas the flexibility to be used in multiple access schemes, which dealswith the assignment of multiple users to a shared communicationresource, has fast adaptation of the waveform to channel variations, andhas effective adaptive modulation and coding (AMC) when CSI is availableat the transmitter. A main benefit of DFT-s-OFDM, compared to amulti-carrier transmission scheme such as OFDM, is reduced variations inthe instantaneous transmit power, implying the possibility for increasedpower-amplifier efficiency. As each sub-carrier carries a portion of thesuperimposed DFT spread data symbols, DFT-s-OFDM may be referred to asSC-FDMA.

DFT-s-OFDM is essentially a single carrier modulation block-basedtransmission scheme with which a lower Peak-to-Average-Power Ratio(PAPR) can be achieved in comparison than OFDM. Its robustness to thefrequency selective fading is also equivalent to OFDM since cyclicprefix (CP) is introduced to avoid inter-symbol interference due tofrequency selective fading.

With a DFT spreading block prior to a subcarrier mapping block and anInverse Discrete Fourier Transform (IDFT) block, which may be referredto as an Inverse Fast Fourier Transform (IFFT) block, DFT-s-OFDM provesto be an effective way of combining the benefits of OFDM with a low PAPRtransmission signal. In particular, the principle of DFT-s-OFDMtransmission applied to an uplink multiple access system is explainedwhereby multiple users transform their time domain symbols independentlyvia the DFT block to get the frequency domain symbols. Each user thenmaps its frequency domain symbols via a subcarrier mapping block onto apre-assigned portion of the overall system spectrum, followed by IDFT(IFFT) and CP insertion as in a typical OFDM transmission. Eachsub-carrier carries a portion of the superimposed DFT spread datasymbols. That is, each sub-carrier contains information of alltransmitted symbols. Note that M represents the number of sub-carriersassigned to a user (i.e., to a WTRU) and N is the total number ofsub-carriers in the system. Thus, an M-sized DFT block is a DFT blockwith a size equal to the number of subcarriers (M) assigned to the WTRUfor an UL transmission.

Subcarrier mapping performed by the subcarrier mapping block can beclassified into two types: localized mapping and distributed mapping. Inlocalized mapping, the DFT outputs are mapped to a subset of consecutivesubcarriers, thereby confining them to only a fraction of the systembandwidth. In distributed mapping, the DFT outputs of the input data areassigned to subcarriers over the bandwidth non-continuously, resultingin zero amplitude for the remaining subcarriers.

Consider that a number of data symbols Nd are to be transmitted by aDFT-s-OFDM transmitter. In one case, Nd is equal to M, i.e., all datasymbols are mapped to the DFT block. The transmit chain of data symbolsNd is first converted from serial data into M symbols of parallel databy which M subcarriers are modulated based on the number of sub-carriers(M). This may be done within the transmit buffer. Thus, a serial toparallel converter takes the serial stream of input data bits Nd andoutputs M parallel streams to a DFT block. In another case, Nd is lessthan M. In this case, some of the inputs of the DFT block may be set tozero, or some known symbols, for example, reference signals.

M points DFT spreading (pre-coding) is performed for M modulatedsub-carriers to distribute the time domain signal over the frequencydomain. Thus, DFT “pre-coding” is performed on the Nd data symbols(i.e., a block of Nd modulation symbols from some modulation alphabet,e.g., QPSK or 16 QAM) by a size-M DFT to transform the Nd data symbolsinto the frequency domain. The output of the DFT block is M. The inputis also M, but all of the M inputs may be data (e.g., when Nd=M) or onlya portion of them (e.g., when Nd<M). By adjusting the transmitter DFTsize M and the size of the block of modulation symbols, the nominalbandwidth of the DFT-s-OFDM signal can be dynamically adjusted.

The modulated symbols output from the DFT block are mapped to orthogonalsubcarriers of the baseband spectrum by the subcarrier mapping block.The sub-carrier mapping allows flexible allocation of signals toavailable sub-carriers.

As used herein, IDFT and IFFT may be used interchangeably with respectto this component of the transmitter since the IDFT uses the inversefast Fourier transform algorithm IFFT. The transformation back to thetime domain is done with an N-point IDFT (N-point IFFT). In particular,the M points of DFT spread modulated signals are fed to N points of anIFFT processor where the Fourier transformation adds the orthogonalspectrum of each subcarrier to the resulting baseband spectrum togenerate OFDM signals. Typically, the IFFT size is selected as N=2^(n)for some integer n to employ FFT algorithm for reducing signalprocessing complexity. It may be assumed that M is an even number andM<N where the unused inputs of the IFFT are set to zero. Finally, theresultant output from the N parallel arms of the IFFT are summed uptogether to produce the OFDM signal. Also similar to OFDM, a cyclicprefix (CP) is preferably inserted for each transmitted block, thepresence of a cyclic prefix allows for straightforward low-complexityfrequency-domain equalization at the receiver side.

As noted above, M may be less than N and the remaining inputs to theIFFT may be set to zero. In this case, the output of the IFFT will be asignal with ‘single-carrier’ properties, i.e., a signal with low powervariations, and with a bandwidth that depends on M. More specifically,assuming a sampling rate, with a sampling frequency Fs, at the output ofthe IFFT, the nominal bandwidth BW of the transmitted signal will beBW=M/N*Fs. Thus, by varying the block size M, the instantaneousbandwidth of the transmitted signal can be varied, allowing forflexible-bandwidth assignment. Furthermore, by shifting the IFFT inputsto which the DFT outputs are mapped by the subcarrier mapping block, thetransmitted signal can be shifted in the frequency domain.

A DFT-s-OFDM receiver, after converting the serial data into paralleldata, would follow the inverse of the DFT-s-OFDM transmitter processesdescribed above, using an FFT block, a reverse subcarrier mapping blockand an IDFT block in succession, before converting the parallel outputsof the IDFT into serial data.

ZT DFT-s-OFDM is described according to one or more embodiments. Thezero tail based waveforms decouple the numerology from the channelcharacteristics. The zero tail duration may be dynamically adapted tothe channel delay spread, without changing the OFDM symbol duration. Inaddition, the zero tail may be used as a gap for beam switching, DL/ULswitching, and interference measurement in mmW channels.

FIG. 13 is a block diagram which illustrates a ZT DFT-s-OFDM transmitter1300, including an M-sized DFT spreading block 1301, a subcarriermapping block 1302 and an N_IFFT-sized IFFT block 1303, each of whichperform functions similarly described above for DFT-s-OFDM. In addition,in ZT DFT-s-OFDM, a zero tail is generated by feeding a number of zerosNh to the head and a number of zeros Nt to the tail of the DFT spreadingblock, as shown in FIG. 13. As described above, the DFT spreading blockspreads the data symbols Nd, the Nh zeros and the Nt zeros between allthe available (allocated) subcarriers. Thus, the number of input datasymbols Nd is equal to M-Nt-Nh, where M represents size of the DFTspreading block 1301. Applying a specific carrier mapping as an example,if the size of the DFT spreading block 1301 is M and the size of theIFFT block 1303 is N_IFFT, at the output of the IFFT there will be the Mdata symbols and (N_IFFT/M-1) interpolated samples between each datasymbol, as shown in FIG. 14.

FIG. 14 illustrates a mechanism for zero tail/head generation. Inparticular, inputs X1-X4 are fed into an M-size DFT block 1401, and anumber of outputs, including X1-X4, are output from the NIFFT-size IFFTblock 1402. N_(IFFT) or NIFFT is the IFFT size performed over the entiresystem bandwidth. Inputs X2 and X3 represent data symbols that aresubsequently output by the IFFT block 1402. If in FIG. 14, X1 is set tozero at the input of the DFT block 1401, the X1 (head) output of theNIFFT-size IFFT block 1402 becomes zero. Similarly, if X4 is set to zeroat the input of the M-size DFT block 1401, the X4 (tail) output of theNIFFT-size IDFT block 1402 becomes zero. Therefore, the zero inputs tothe DFT block 1401 will be distributed on the head and tail of thesignal at the output of the IFFT.

However, the tail does not become exactly zero due to the interpolatedsamples. In addition, since the interpolated samples are data dependent,the zero tail is different from one DFT-s symbol to the next. Therefore,the cyclic property is not preserved, which leads to a bit error floorat high SNR for high order modulations.

In summary, one shortcoming of the ZT DFT-s OFDM signal is that thenon-perfect zero tail breaks the cyclic property of the OFDM signal andcreates Inter-Symbol Interference (ISI). This results in a bit errorrate (BER) floor at high signal-to-noise ratio (SNR) in high delayspread channels.

The ZT solution shown in FIG. 13 is defined for DFT-s OFDM only. Thus,other high complexity solutions to generate ZT for OFDM are providedherein.

Unique Word (UW) OFDM is a method used to eliminate the waveformoverhead due to the CP, by replacing the CP with a fixed pilot, referredto as “Unique Word”. The unique word may be used for synchronization,channel estimation and phase tracking purposes. In this case, the CP isnot required, as the UW acts a guard interval against ISI and maintainsthe cyclic property of the signal.

In one method of generating the UW OFDM, the tail of the OFDM symbol atthe output of the IFFT block is forced to zero. This may be achievedusing a redundant signal at the input of the IFFT, whereby the redundantsignal is generated by precoding the data symbols and mapped to acertain set of subcarriers. The set of subcarriers should be carefullyselected so that the power used for the redundant data does not becomeexcessive. Once the tail is forced to zero, the deterministic UWsequence may be added to the zero tail to facilitate tasks such assynchronization, channel estimation, etc.

FIG. 15 shows a UW OFDM transmitter 1500 according to one or moreembodiments. Modulation data symbols d are input to the transmitter1500. The data symbols d are passed on to a redundant data generator (T)1501, which generates redundant data r, and a permutation matrix (P)1502. The permutation matrix 1502 receives a number of data symbols Ndand a number of redundant data symbols Nr. The modulation data symbols dand redundant data r are mapped to the IFFT block 1504 after processedby the permutation matrix 1502, whose task is to map the data d andredundant data r to the correct subcarriers, and block (B) 1503, whosetask is to insert a null set of (zero) subcarriers for the guard bands.The transmitted signal with zero tail may be written as

${{F_{NIFFT}^{H}{{BP}\begin{bmatrix}d \\r\end{bmatrix}}} = \begin{bmatrix}x_{d} \\0\end{bmatrix}},$where block B 1503 inserts the zero subcarriers for the guard bands, andF_(NIFFT) ^(H) is the FFT matrix (of size N_IFFT×N_IFFT), and thesuperscript H indicates the Hermitian (transpose conjugate) of thematrix. The formula describes in matrix form the processing steps at thetransmitter, specifically:

$P\begin{bmatrix}d \\r\end{bmatrix}$means the permutation matrix applied to the input vector of data andredundant symbols;

${BP}\begin{bmatrix}d \\r\end{bmatrix}$describes the next step, i.e., the sub-carrier mapping functionperformed by block B 1503, which can also be expressed as matrixmultiplication; and

$F_{NIFFT}^{H}{{BP}\begin{bmatrix}d \\r\end{bmatrix}}$describes the next step, which is the IFFT processing (that can also beexpressed as matrix multiplication, i.e., the IFFT matrix times thevector at the matrix input, which is the vector generated as output ofsecond step above. Writing,

${M = {{F_{NIFFT}^{H}{BP}} = \begin{bmatrix}M_{11} & M_{12} \\M_{21} & M_{22}\end{bmatrix}}},$the redundant data may be computed as r=Td where T=−M₂₂ ⁻¹M₂₁.

A unique word block 1505 generates and inserts a unique word for eachtransmitted block, and the OFDM signal NFFT is converted to a serialdata symbols by a parallel to serial converter 1506.

The Tx and Rx complexity for the UW OFDM signal are high. For eachresource allocation, the permutation matrix P used in 1502 needs to beoptimized to minimize the power of the redundant subcarriers. Thisresults in both computational complexity at the transmitter, and insignaling overhead, as knowledge of the permutation matrix is requiredat the receiver, in order to decode the data. Due to the need tooptimize the permutation matrix for each resource allocation, support offrequency domain scheduling and multi-user is difficult with UW-OFDM.

Thus, embodiments disclosed herein may provide waveform(s) thatdynamically change the guard interval duration to support differentchannel delay spreads without changing the numerology. Embodiments mayfurther address one or more shortcomings of existing ZT or UW waveforms.These embodiments may eliminate an error floor of ZT DFT-s OFDM andimprove the BER performance, if possible, and provide flexible supportfor frequency domain scheduling and multi-user to UW-OFDM, whilereducing the overall complexity. Embodiments disclosed herein may definea flexible framework that supports both DFT-s-OFDM, and OFDM basedwaveforms.

Embodiments disclosed herein include an enhanced ZT solution (eZT) forDFT-s-OFDM, an eZT solution for OFDM, and system aspects for ZT/UWwaveforms. These embodiments may be implemented in a transmitter, areceiver and/or a transceiver, and in combination with a processor, of aWTRU and/or any type of base station (e.g., eNode-B (eNB), mmW eNB (mB),Small Cell mmW eNB (SCmB), etc.), collectively referred to herein as awireless communication device.

The eZT solution for DFT-s-OFDM provides one or more of the following:an iterative approach for exact zero-tail generations; time-domain tailcancellation prior to guard band insertion including UW support usingeZT DFT-s-OFDM; extending the time-domain tail cancellation prior toguard band insertion for multi-user support; time-domain tailcancellation at the IFFT output after guard band insertion; a receiverstructure including an optimal Linear Minimum Mean Square Error (LMMSE)and a reduced complexity receiver; and performance metrics includingBER, PAPR, and out-of-band (OOB).

The eZT solution for OFDM includes one or more of the following: aniterative approach for exact zero-tail cancellation; time-domain tailcancellation prior to guard band insertion; tail cancellation using a ZTDFT-s approach and a UW-ZT approach; multi-user support; and performancemetrics. System aspects for ZT/UW waveforms are further disclosed.

The set of examples disclosed herein may have a number of advantagesover the existing ZT DFT-s-OFDM and UW OFDM waveforms. The eZTDFT-s-OFDM solution may significantly reduce the tail power as comparedto ZT DFT-s-OFDM, thus improving the performance at high SNR and highorder modulation. This is an important enabler for reaching the highpeak data rates expected for 5G. The eZT ODFM solution has a reducedcomplexity transmitter architecture, that makes it easier to supportfrequency domain (and multi-user) scheduling, thus solving the problemexperienced by the current UW OFDM waveform. The disclosed eZT solutionhas a flexible, modular architecture that supports both DFT-s-OFDM andOFDM. Due to the fact that the disclosed solution significantly reducesthe tail power compared to ZT, it may be used to support UW insertion,for both DFT-s-OFDM and OFDM. The disclosed solution has low out-of-band(OOB) emissions, significantly lower than the traditional CP DFT-s-OFDMor CP OFDM, making it a promising solution for 5G.

In an enhanced ZT embodiment for DFT-s-OFDM, an iterative approach forexact zero tail generation is provided herein. In this low complexityembodiment, the exact zero tail is generated by adding a low powercancellation signal to data sub-carriers, whereby the low powercancellation signal is generated by selecting the Nzt time-domainsamples, spreading them with a DFT block of size Nzt, then mapping thecancellation signal in an interleaved fashion to the in-bandsubcarriers, and super-imposing the cancellation signal on the datasubcarriers, as shown in FIG. 16.

FIG. 16 is a flow diagram which illustrates an iterative approachimplemented in a transmitter for eZT generation for DFT-s-OFDM. Togenerate a low power tail cancellation signal of Nzt time domain samplesY13, Y14, Y15 and Y16 at the IFFT output, shown by way of example asY13, Y14, Y15 and Y16 in step 1 of FIG. 16, Nt zero symbols may beplaced at the tail of the input data symbols (d), as inputs to the DFTblock 1601. Additionally, as an enhancement, Nh zero symbols may beplaced at the head of the data symbols (d) at the input of the DFT block1601, to further reduce the tail power. If the zero head is not used, Nhmay be set to 0.

The frequency-domain output of the DFT block 1601 in step 1 is mapped tothe input of the size N IFFT block 1603, by means of a (non-interleave)sub-carrier mapping block 1602. The sub-carrier mapping block 1602 maymap the DFT outputs to consecutive sub-carriers at the IFFT block 1603input, in order to preserve the single carrier property of the signal.

In Step 2 of the processing shown in FIG. 16, Nzt time domain samples(i.e., sub-vector) at the output of the IFFT block 1603, shown by way ofexample as Y13, Y14, Y15 and Y16 in step 1 of FIG. 16, are sign inverted(e.g., −Y13, −Y14, −Y15 and −Y16) by an inverter, may be normalized(e.g., multiplied by a normalization factor), and fed to the input of asize Nzt DFT block 1605. The outputs of the size Nzt DFT block 1605 aremapped by an interleave subcarrier mapping block 1606 in an interleavedfashion to the size N IFFT block 1607, whereby zeros are inserted on

$\frac{N}{N_{zt}} - 1$consecutive sub-carriers between each output of the Nzt size DFT block1605, where

$\frac{N}{N_{zt}}$is an integer value. As a result of this interleaved sub-carriermapping, the output of the IFFT block 1607 is a replica of the signal atthe input of the DFT block 1605, repeated

$\frac{N}{N_{zt}}$times. Using the example shown in Step 2 of FIG. 16, the output of theIFFT block 1607 is comprised of the vector [−Y13, −Y14, −Y15, −Y16],repeated

$\frac{N}{N_{zt}}$times.

In Step 3 of the processing, the outputs 1604 and 1608 of the IFFTblocks 1603 and 1607, respectively, in Steps 1 and 2 are summed togetherby a summing block 1609, thus resulting in an exact zero tail of lengthNzt samples, at the output of the summing block 1609. It will beappreciated that the Nzt time domain samples Y13, Y14, Y15 and Y16 maynot be inverted, but instead, the low power cancellation signal (outputof Step 2) may be subtracted from the data signal (output of Step 1) instep 3.

The time-domain signal y, generated at the output of Step 3 by thesumming block 1609, is further processed by a guard insertion block 1610before being transmitted on the channel. The guard insertion may beperformed either in the frequency domain, or in the time domain. Thetail, in general, may not be exactly zero after guard band insertion.

An example of guard band insertion performed in the frequency domain isshown in FIG. 17 and an example of guard band insertion performed in thetime domain is shown in FIG. 18.

The following notations are used herein:

F_(N) ∈

^(N×N) is an N size FFT matrix (normalized),

F_(N) ^(H) denotes the N size IFFT matrix,

I_(N) ∈

^(N×N) is an identity matrix,

O_(N) ₁ _(×N) ₂ ∈

^(N) ¹ ^(×N) ² is an N₁×N₂ zero matrix,

P_(d) ∈

^(N×M) is the sub-carrier mapping matrix used by the subcarrier mappingblock 1602 for the data part of the signal in Step 1 of FIG. 16, and

P_(c) ∈

^(N×N) ^(zt) is the sub-carrier mapping matrix used by the subcarriermapping block 1606 for the cancellation part of the signal in Step 2 ofFIG. 16.

As explained previously, the Nzt outputs of the DFT block 1605 aremapped in a uniformly interleaved fashion, to the inputs of the N-sizeIDFT (IFFT) block 1607. Thus the P_(c) matrix may be expressed asfollows:

$\begin{matrix}{{P_{c}\left( {n,m} \right)} = \left\{ \begin{matrix}{1,} & {{{{for}\mspace{14mu} n} = {{{k \cdot \frac{N}{N_{zt}}}\mspace{14mu}{and}\mspace{14mu} m} = k}},{0 \leq k \leq {N_{zt} - 1}}} \\{0,} & {otherwise}\end{matrix} \right.} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In an example, for N=16 and Nzt=4, the P_(c) matrix is defined as:

$\begin{matrix}{P_{c} = \begin{bmatrix}1 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 1 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0\end{bmatrix}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Nzt is the desired length of the zero tail (in samples). M is the DFTsize. N is the number of used sub-carriers. Nt is the number of symbolsset to zero at the tail at the DFT input.

${N_{zt} = {N_{t}\left\lfloor \frac{N}{M} \right\rfloor}},$where [A] denotes a “floor” operation, for example, the largest integersmaller or equal to A. N_(IFFT) is the IFFT size performed over theentire system bandwidth. B ∈

^(N) ^(IFFT) ^(×N) is the matrix used for sub-carrier mapping, whichincludes the guard band insertion.The size M vector at the input of the DFT 1601 may be expressed as:

$x = \begin{bmatrix}0_{N_{h} \times 1} \\d \\0_{N_{t} \times 1}\end{bmatrix}$where d ∈

^(M−N) ^(h) ^(−N) ^(t) ^()×1) is a vector of complex data modulationsymbols.

At the output of the N-size IFFT 1603 of FIG. 16, the last Nzt samplesmay be used to generate the tail cancellation signal, as follows. Lety_(d)=[y₀ y₁ . . . y_(N−1)]^(T), y_(d) ∈

^(N×1) be the vector at the output of the N-size IFFT 1603, andy_(temp_c) ∈

^(N) ^(zt) ^(×1) be the vector of the last Nzt samples of y_(d),y_(temp_c)=[y_(N−N) _(zt) . . . y_(N−1)]^(T). The last Nzt samples usedin the cancellation process (y_(temp_c)) may be expressed in terms ofthe vector y_(d) at the output of the IFFT 1603 as: y_(temp_c)=Cy_(d)where C ∈

^(N) ^(zt) ^(×N) is a matrix that may be used to select the last Nztsamples of y_(d). The C matrix may be expressed as: C=[0_(N) _(zt)_(×(N−N) _(zt)) I_(N) _(zt) ]. Using the previous notations, the signaly_(d) at the output of the N-size IFFT 1603 of step 1 may be written as:y_(d)=F_(N) ^(H)P_(d)F_(M)x.

Similarly, when applying the sign-inverted −y_(temp_c) samples to theinput of the Nzt size DFT 1605, followed by the sub-carrier mappingoperation P_(c) of the mapping block 1606, and followed by the N-sizeIFFT 1607, the cancellation signal (scaled by a factor of

$\left. \sqrt{\frac{N}{N_{zt}}} \right)$at the output of Step 2 may be written as:

$\begin{matrix}{y_{c} = {{{- \sqrt{\frac{N}{N_{zt}}}}F_{N}^{H}P_{c}F_{N_{zt}}y_{{temp}\_ c}} = {{{- \sqrt{\frac{N}{N_{zt}}}}F_{N}^{H}P_{c}F_{N_{zt}}{Cy}_{d}} = {{- \sqrt{\frac{N}{N_{zt}}}}F_{N}^{H}P_{c}F_{N_{zt}}{CF}_{N}^{H}P_{d}F_{M}x}}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Next, the data signal y_(d) and the cancellation signal y_(c) are summedtogether by summing block 1609, resulting in the time-domain signaly=y_(d)+y_(c) with the last Nzt samples equal zero. By substitutingy_(d) and y_(c) in the previous equation, the time-domain signal y maybe rewritten as:

$\begin{matrix}{y = {{F_{N}^{H}\left( {I_{N} - {\sqrt{\frac{N}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{N}^{H}}} \right)}P_{d}F_{M}x}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

As previously indicated, once the tail cancellation is performed in timedomain by the summing block 1609, the guard bands may be inserted by theguard band insertion block 1610 before the signal is transmitted.

In an example of the frequency domain guard band insertion, a guard bandinsertion block 1700 is shown in FIG. 17. The signal y at the output ofstep 3 may be passed through an N-size DFT block 1701, followed by guardband insertion, which may be modeled for analysis purposes as amultiplication by matrix B by a subcarrier mapping block 1702, and anIFFT operation over the entire system bandwidth by size NIFFT IFFT block1703, followed by a parallel to serial conversion by parallel to serialconverter block 1704. The time domain signal at the transmitter outputmay be expressed as:x_(t)=F_(N) _(IFFT) ^(H)BF_(N)y  Equation 5

By substituting y in the previous equation, the transmitted signal x_(t)becomes:

$\begin{matrix}{x_{t} = {F_{N_{IFFT}}^{H}{B\left( {I_{N} - {\sqrt{\frac{N}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{N}^{H}}} \right)}P_{d}F_{M}x}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

This expression for the time domain transmitted signal will be usedbelow to derive the receiver structure for the eZT DFT-s-OFDM signal.

In an example of the time domain guard band insertion, a guard bandinsertion block 1800 is shown in FIG. 18. The signal y at the output ofstep 3 may be passed through an upsampler 1801, a filter 1802, and adownsampler 1803, and the transmitted signal x_(t) is output.

Time-domain tail cancellation prior to guard band insertion is describedin more detail below. In an embodiment, a low complexity method togenerate exact zero tail in time domain is provided, whereby a low powercancellation signal yc is subtracted from the data signal yd prior toguard band insertion, and the cancellation signal yc is generated byrepeating Nzt samples of the data. An example is illustrated in FIG. 19,where, in the example, the tail that needs to be cancelled is comprisedof the vector [Y13 Y14 Y15 Y16], which is labeled a for convenience.

FIG. 19 is a block diagram which illustrates time-domain tailcancellation prior to guard band insertion according to one or moreembodiments. The transmitter illustrated in FIG. 19 includes an M sizeDFT block 1901, a (non-interleave) subcarrier mapping block 1902 and anN size IFFT block 1903, as similarly described in step 1 of FIG. 16, atail cancelation block 1909, as similarly described in step 3 of FIG.16, and a guard band insertion block 1910, as similarly described at thefinal output (1610) of FIG. 16. Further, the cancelation signalcomprised of the vector [−α −α . . . −α], is generated by repeating thetail part (alpha vector) N/Nzt times. The tail cancelation block 1909generates the cancellation signal [−α −α . . . −α] and adds it to theoutput of the IFFT block (1903). Here, like numerals correspond to likeelements and the functionality of each block is not repeated forconciseness.

UW support using eZT DFT-s-OFDM is further provided in one or moreembodiments. For example, a UW DFT-s-OFDM signal is generated, by addingin the time domain a UW to the exact zero-tail generated by eZTDFT-s-OFDM (i.e., the UW is added prior to guard band insertion).

FIG. 20 is a block diagram which illustrates UW support using eZTDFT-s-OFDM. The transmitter illustrated in FIG. 20 includes an M sizeDFT block 2001, a subcarrier mapping block 2002 and an N size IFFT block2003, as similarly described in step 1 of FIG. 16, a tail cancelationblock 2009, as similarly described in step 3 of FIG. 16, and a guardband insertion block 1700 and 1800, as similarly described in FIGS. 17and 18. Further, the cancelation signal comprised of the vector [−α −α .. . −α], is generated by repeating the tail part (alpha vector) N/Nzttimes. The tail cancelation block 2009 generates the cancellation signal[−α −α . . . −α], and adds it to the output of the IFFT block (2003), asshown in process 2009 a performed by the tail cancelation block 2009. Inaddition, a unique word is added by adder 2011 to the time-domain signaly, and the guard band is inserted by guard band insertion block 1700 or1800 to generate transmitted signal xt. Block 1900 a further illustratesthe process of generating the time-domain signal y, as previouslydescribed. Here, like numerals correspond to like elements and thefunctionality of each block is not repeated for conciseness.

An architecture for multi-user support is further provided in FIG. 21 inwhich redundant transmitter structures 2100(1), 2100(2) . . . 2100(k),as similarly described in reference to FIG. 19, are provided for eachuser to generate a multi-user transmission. Here, a transmitter (e.g., abase station transmitter) uses the enhanced zero-tail mechanism togenerate user specific exact zero-tail for DL DFT-s-OFDM multi-usertransmission, whereby, first, the tail cancellation is performed peruser, then the multi-user signal for transmission is generated by addingthe individual users signals together by adder 2112, and followed byguard band insertion via guard band insertion 2110 for completion of thecomposite signal. The block diagram of FIG. 21 shows how user specificZT lengths may be supported. For example, the number of zerosub-carriers that may be placed at the tail of the input data symbolsmay vary or be the same for each user, and the size of each DFT blockmay also be the same or different.

As the tail cancellation is performed per user, the solution shown inFIG. 21 enables setting different lengths of zero tail for individualusers.

Time-domain tail cancellation at the IFFT output after guard bandinsertion is provided as another embodiment. Here, tail cancellation maybe performed in the time domain at the output of an IFFT block, afterthe guard band insertion operation, as shown in FIG. 22. The transmitterillustrated in FIG. 22 includes an M size DFT block 2201, a subcarriermapping block 2202 and an N_(IFFT) size IFFT block 2203, as similarlydescribed in FIG. 17, a tail cancelation block 2209, as similarlydescribed in step 3 of FIG. 16, and a guard band insertion block 2210,as similarly described in FIGS. 16 and 17 with the exception that theguard band insertion block 2210 is disposed between the subcarriermapping block 2202 and the N_(IFFT) size IFFT block 2203. Further, thecancelation signal comprised of the vector [0, 0 . . . −α], is generatedby multiplying the tail part (alpha vector) is taken by −1 togenerate—alpha. The tail cancelation block 2209 generates thecancellation signal [0, 0 . . . −α] and adds it to the output of theIFFT block (2203). A parallel to serial converter 2213 receives thetime-domain signal y from the tail cancelation block 2209 and convertsinto serial data symbols. Here, like numerals correspond to likeelements and the functionality of each block is not repeated forconciseness.

In this embodiment, it is important to feed Nt and Nh zeros for the tailand head at the input to the DFT. This way, the Nzt tail samples at theoutput of the IFFT block have low power, which helps reduce the spectrumregrowth that may occur as a result of time domain tail cancellation ofNzt tail samples.

In addition to the transmitter structures described above, receiverstructures for eZT DFT-s-OFDM are also provided herein. For example,FIG. 23 illustrates a block diagram of a high level receiver 2300according to one or more embodiments. The structure of the receiver 2300may be derived starting from the expression of the time domaintransmitted signal which is repeated for convenience:

$\begin{matrix}{x_{t} = {F_{N_{IFFT}}^{H}{B\left( {I_{N} - {\sqrt{\frac{N}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{N}^{H}}} \right)}P_{d}F_{M}x}} & {{Equation}\mspace{14mu} 7}\end{matrix}$

The frequency domain channel response is denoted by Λ: ∈

^(N) ^(IFFT) ^(×N) ^(IFFT) , where Λ is a diagonal matrix whose diagonalelements represent the complex channel gains per subcarrier. With thisnotation, the time domain signal r_(t) at the receiver input may beexpressed as:r _(t) =F _(N) _(IFFT) ^(H) ΛF _(N) _(IFFT) x _(t) +n′  Equation 8where n′ is the time-domain noise vector. The first stages of thereceiver processing of receiver 2300 are a serial to parallel conversion2301, followed by a FFT processing by an DFT block 2302, and asub-carrier de-mapping by a sub-carrier de-mapping block 2303, asillustrated in FIG. 23.

The sub-carrier de-mapping operation by the sub-carrier de-mapping block2303 is the inverse of the sub-carrier mapping performed at thetransmitter side, and in matrix form it is simply expressed as B^(T), sothe frequency domain signal at the sub-carrier de-mapping output r is:r=B ^(T) F _(N) _(IFFT) r _(t) +n  Equation 9where n is the frequency-domain noise vector. After substituting r_(t)in the previous equation, r becomes:

$r = {{{B^{T}F_{N_{IFFT}}F_{N_{IFFT}}^{H}\Lambda\; F_{N_{IFFT}}x_{t}} + n} = {{{B^{T}\Lambda\; F_{N_{IFFT}}x_{t}} + n} = {{B^{T}\Lambda\; F_{N_{IFFT}}F_{N_{IFFT}}^{H}{B\left( {I_{N} - {\sqrt{\frac{N}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{N}^{H}}} \right)}P_{d}F_{M}x} + n}}}$

The received signal r at the output of the sub-carrier de-mapping block2303 may further be expressed as:

$\begin{matrix}{r = {{{B^{T}\Lambda\;{B\left( {I_{N} - {\sqrt{\frac{N}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{N}^{H}}} \right)}P_{d}F_{M}x} + n} = {{HGx} + n}}} & {{Equation}\mspace{14mu} 11}\end{matrix}$where the following notations are used: H=B^(T)ΛB, H ∈

^(N×N) represents the effective channel response matrix over theoccupied sub-carriers, and G=

${\left( {I_{N} - {\sqrt{\frac{N}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{N}^{H}}} \right)P_{d}F_{M}},$G ∈

^(N×M) is a matrix that depends on the sub-carrier mapping matrices forthe data and the cancellation signals (P_(d) and P_(c), respectively),as well as on the FFT matrices of the corresponding sizes. It should benoted that for a given (fixed) resource allocation, the G matrix isconstant.

To calculate the G matrix, only the resource allocation and the lengthof the zero tail need to be signaled to the receiver. Based on thesignaled resource allocation, the receiver determines the datasub-carrier mapping matrix P_(d), the FFT matrices F_(M) and F_(N).Additionally, once the length of the zero tail Nzt is known, thereceiver determines the sub-carrier mapping matrix for the tailcancellation signal, P_(c), the FFT matrix F_(N) _(zt) and thus it maycalculate the G matrix using the equation above.

The receiver 2300 may further include an optimal LMMSE receiver 2304.The optimal LMMSE receiver 2304 is configured to retrieve thetransmitted vector x as the LMMSE. Corresponding to the received signalr=HGx+n, the optimal LMMSE receiver 2304 may be expressed as:x _(est)=(G ^(H) H ^(H) HG+σ ² I)⁻¹ G ^(H) H ^(H) r  Equation 12

In the previous equation, σ²represents the estimated noise variance.

As mentioned previously, the G matrix is only a function of the resourceallocation, and does not depend on the channel. Therefore, for a fixedresource allocation, the G matrix is fixed.

Moreover, for slowly varying channels, which may be the case for indoorpropagation channels, the channel response may not change significantly,so matrix H may change slowly. As a result, once the LMMSE filtercoefficients are calculated, they may be reused for a longer time, whichmay help lower the receiver complexity.

The receiver 2300 may further include a reduced complexity receiver2305. The reduced complexity receiver 2305 may be derived for thereceived signal r=HGx+n as a two-step approach, whereby the first stepis a 1-tap equalizer 2306 that equalizes the channel (recall that the Hmatrix is diagonal), and the filter 2307 for the second step inverts thetransmit processing chain that includes the cancellation signal. Morespecifically, the reduced complexity receiver 2305 consists in the twosteps described herein. Step 1: x_(est_1=)(H^(H)H+σ²I)⁻¹H^(H)r and Step2: x_(est=)(G^(H)G)⁻¹G^(H)x_(est_1).

The reduced complexity receiver 2305 is lower in complexity than theoptimal LMMSE receiver 2304 because the first step of the processing orchannel equalization is a simple 1 tap channel equalization, and the 2ndstep needs to be performed only when the resource allocation changes,for example, when the G matrix changes.

Both the optimal LMMSE receiver 2304 and the reduced complexity receiver2305 may be used to simulate the performance of eZT DFT-s-OFDM asdisclosed herein.

Performance metrics are shown herein for one or more eZT DFT-s-OFDMembodiments, including for the BER performance, peak to average powerratio (PAPR), out of band (OOB) emissions, as well as a sampleperformance for the multi-user case.

The raw BER performance of eZT DFT-s-OFDM for three different values ofM, and with a high delay spread channel and 64-QAM modulation, is shownin FIG. 24. The eZT performance has been evaluated using the optimalLMMSE receiver 2304, as well as the reduced complexity receiver 2305.The performance of ZT DFT-s-OFDM (non-enhanced) is also illustrated forcomparison purposes. For all simulation results, the total transmissionpower is normalized and SNR is defined as symbol energy (Es) to noise(No) ratio (Es/No).

As may be seen in FIG. 24, for high delay spread channels, the ZTDFT-s-OFDM exhibits an error floor, which is due to the fact that the ZTDFT-s-OFDM does not have a perfect zero tail. This tail breaks thecyclic property of the OFDM signal and creates ISI. This limits theperformance in high delay spread channels and manifests itself in anerror floor that occurs with higher order modulation symbols. Bycontrast, the eZT DFT-s-OFDM system does not exhibit this error floor,as shown by the optimal LMMSE receiver results and the reducedcomplexity receiver results. Use of the optimal LMMSE receiver 2304results in a significant performance improvement over ZT, of 2.5 to 4 dBSNR improvement at BER=10−2, as well as in the elimination of the errorfloor. The reduced complexity receiver 2305 also eliminates the errorfloor of the ZT.

Since the cancellation signal yc used to generate the zero tail is lowpower, the cancellation signal yc is not expected to increase the PAPRas compared to the ZT DFT-s-OFDM. The Nzt samples may be seen at theoutput of the N-size IFFT 1603 in Step 1, FIG. 16. This has beenconfirmed by simulations, the results of which are captured in FIG. 25,where it may be seen that the PAPR of eZT DFT-s-OFDM is the same as forZT DFT-s-OFDM.

Additionally, the disclosed eZT method preserves the advantage of theZT, in that it has a low out-of-band emission. As a result, eZTDFT-s-OFDM may be used as an alternative to filter-based OFDM such asFiltered-OFDM (F-OFDM) or Universal Filtered Multi-Carrier (UFMC), andmay be applicable to flexible air-interfaces for sub-6 GHz frequencies.The simulated OOB performance of the disclosed eZT DFT-s-OFDM embodimentis shown in FIG. 26, where it may be seen that the OOB emission issignificantly lower compared to the traditional CP DFT-s-OFDMembodiment.

The time-domain illustration of the eZT DFT-s-OFDM signal shown in FIG.27 confirms that the tail of the disclosed eZT embodiment is 20-30 dBlower than the tail of ZT DFT-s-OFDM.

A simulation was run for the multi-user scenario described in FIG. 21.The simulation results, presented in FIG. 28 confirm that the multi-userperformance of the disclosed embodiment matches the single userperformance.

FIG. 29 illustrates a step block diagram of another eZT solution forOFDM in which an iterative approach for exact zero tail generation isused. In a low complexity solution, the exact zero tail is generated byadding a cancellation signal to data sub-carriers, whereby thecancellation signal is generated by selecting the Nzt time-domainsamples, spreading them with DFT of size Nzt, then mapping thecancellation signal in an interleaved fashion to the in-bandsubcarriers, as similarly described in reference to FIG. 16. However, inthe method presented in FIG. 29, the subcarriers on which thecancellation signal is mapped, do not carry modulated data symbols. Thatis, the cancellation signal and the modulated data symbols aretransmitted on disjoint subcarriers.

FIG. 29 is a step block diagram which illustrates an iterative approachfor exact zero tail generation for OFDM. In Step 1, an OFDM signal 2904is generated by mapping modulated data symbols to M allocatedsubcarriers in a subband. In particular, zeros are input in thefrequency domain to an interleave subcarrier mapping block 2902 and areinterleaved to a portion of the subcarriers by the interleave subcarriermapping block 2902. Data symbols are also input to the interleavesubcarrier mapping block 2902 and fill the remaining subcarriers thathave not been mapped to by the zeros. Thus, data and zeros areinterleaved with each other at the output of the interleave subcarriermapping block 2902. For example, data symbols and zeros may be mappedaccordingly: 0, d1, d2, d3, 0, d4, d5, . . . , etc. Thus, a subset ofthe subcarriers that may be uniformly interleaved over the subband isleft empty, for example, wherein data is not mapped to those subcarriersby the mapping block 2902. Instead, as shown in Step 1 of FIG. 29, zerosare mapped to the input of the IFFT block 2903 where these emptysubcarriers are located.

In Step 2 of the processing, Nzt time domain samples at the output ofthe IFFT block 2903, shown by example as Y13, Y14, Y15 and Y16 in Step 1of FIG. 29, are sign inverted by an inverter, normalized by anormalization factor, and fed to the input of a size Nzt DFT operationperformed by DFT block 2905. The outputs of the size Nzt DFT block 2905are mapped in an interleaved fashion to the size M IFFT block 2907 byinterleave subcarrier mapping block 2906, whereby zeros are inserted on

$\frac{M}{N_{zt}} - 1$consecutive sub-carriers between each output of the Nzt size DFT block2905. As a result of this interleaved sub-carrier mapping, the IFFToutput 2908 is a replica of the signal at the input of the DFT block2905, repeated

$\frac{M}{N_{zt}}$times. Using the example shown in Step 2 of FIG. 29, the IFFT output2908 consists of the vector [−Y13, −Y14, −Y15, −Y16], repeated

$\frac{M}{N_{zt}}$times.

In Step 3 of the processing, the outputs 2904 and 2908 of the IFFTblocks 2903 and 2907 in Steps 1 and 2 are summed together by a summingblock 2909, thus resulting in an exact zero tail of length Nzt samples,at the output of summing block 2909. It will be appreciated that the Nzttime domain samples Y13, Y14, Y15 and Y16 may not be inverted, butinstead, the low power cancellation signal (output of Step 2) may besubtracted from the data signal (output of Step 1) in Step 3.

The signal y generated at the output of Step 3 is further processed by aguard insertion block 2910 before being transmitted on the channel. Theguard insertion may be performed either in the frequency domain, or inthe time domain as previously described in reference to FIGS. 16-18.

An example of guard band insertion performed in the frequency domain isshown in FIG. 30, similar to FIG. 17. An example of guard band insertionperformed in the time domain is shown in FIG. 31, similar to FIG. 18.

The following notations are described as used herein. F_(M) ∈

^(M×M): M size FFT matrix (normalized). Thus F_(M) ^(H) denotes the Msize IFFT matrix. I_(M) ∈

^(M×M) is the identity matrix. O_(N) ₁ _(×N) ₂ ∈

^(N) ¹ ^(×N) ² is a N1×N2 zero matrix. P_(d) ∈

^((M)×(M−Nzt)) is a sub-carrier mapping matrix, used for the data partof the signal in Step 1 of FIG. 29. P_(c) ∈

^(M×Nzt) is a sub-carrier mapping matrix, used for the cancellation partof the signal in Step 2 of FIG. 29. Nzt is the desired length of thezero tail (in samples). N_(IFFT) is the IFFT size performed over thesystem bandwidth. B ∈

^(N) ^(IFFT) ^(×M) is the matrix used for guard band insertion.

At the output of the M-size IFFT 2903 of FIG. 29, the last Nzt samplesmay be used to generate the tail cancellation signal yc, as follows. Lety_(d)=[y₀ y₁ . . . y_(M−1)]^(T), y_(d) ∈

^(M×1) be the vector at the M-size IFFT output of IFFT 2903, andy_(temp_c) ∈

^(N) ^(zt) ^(×1) the vector of the last Nzt samples of y_(d),y_(temp_c)=[y_(M−N) _(zt) y_(M−1)]^(T). The last Nzt samples used in thecancellation process (y_(temp_c)) may be expressed in terms of thevector y_(d) at the output of the IFFT 2903 as:Y_(temp_c)=Cy_(d)  Equation 13where C ∈

^(N) ^(zt) ^(×M) is a matrix that may be used to select the last Nztsamples of y_(d). The C matrix may be expressed as:C=[O_(N) _(zt) _(×(M−N) _(zt) ) I_(N) _(zt) ]  Equation 14

The signal y_(d) at the output of the M-size IFFT 2903 of Step 1 may bewritten as:y_(d)=F_(M) ^(H)P_(d)x  Equation 15

Similarly, when applying the sign-inverted −y_(temp_c) samples to theinput of the Nzt size DFT 2905, followed by the sub-carrier mappingoperation P_(c) by mapping block 2906 and the M-size IFFT 2907, thecancellation signal (scaled by a factor of

$\left. \sqrt{\frac{M}{N_{zt}}}\; \right)$at the output of Step 2 may be written as:

$\begin{matrix}{y_{c} = {{{- \sqrt{\frac{M}{N_{zt}}}}F_{M}^{H}P_{c}F_{N_{zt}}y_{{temp}\_ c}} = {{{- \sqrt{\frac{M}{N_{zt}}}}F_{M}^{H}P_{c}F_{N_{zt}}{Cy}_{d}} = {{- \sqrt{\frac{M}{N_{zt}}}}F_{M}^{H}P_{c}F_{N_{zt}}{CF}_{M}^{H}P_{d}x}}}} & {{Equation}\mspace{14mu} 16}\end{matrix}$

Next, the data signal y_(d) and the cancellation signal y_(c) are summedtogether by summing block 2909, resulting in the time-domain signaly=y_(d)+y_(c) with the last Nzt samples equal zero. By substitutingy_(d) and y_(c) in the previous equation, the time-domain signal y maybe rewritten as:

$\begin{matrix}{y = {{F_{M}^{H}\left( {I_{M} - {\sqrt{\frac{M}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{M}^{H}}} \right)}P_{d}x}} & {{Equation}\mspace{14mu} 17}\end{matrix}$

As previously indicated, once the tail cancellation is performed in thetime domain, the guard bands may be inserted by guard band insertionblock 2910 before the signal may be transmitted.

In an example of frequency domain guard band insertion by a guard bandinsertion block 3000 as shown in FIG. 30, the signal y at the output ofStep 3 may be passed through an M-size DFT 3001, followed by guard bandinsertion, which may be modeled for analysis purposes as amultiplication by matrix B by a subcarrier mapping block 3002, and anIFFT operation over the entire system bandwidth by size N IFFT block3003, followed by a parallel to serial conversion by parallel to serialconverter block 3004. The time domain signal x_(t) at the transmitteroutput may be expressed as:x_(t)=F_(N) _(IFFT) ^(H)BF_(M)y  Equation 18

By substituting y in the previous equation, the transmitted signalbecomes:

$\begin{matrix}{x_{t} = {F_{N_{IFFT}}^{H}{B\left( {I_{M} - {\sqrt{\frac{M}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{M}^{H}}} \right)}P_{d}x}} & {{Equation}\mspace{14mu} 19}\end{matrix}$

This expression for the time domain transmitted signal will be used asdisclosed to derive the receiver structure for the eZT OFDM signal.

In an example of the time domain guard band insertion, a guard bandinsertion block 3100 is shown in FIG. 31. The signal y at the output ofstep 3 may be passed through and upsampler 3101, a filter 3102, and adownsampler 3103, and the transmitted signal x_(t) is output.

In one or more embodiments, a low complexity method to generate exactzero tail in time domain is provided in order to achieve time-domaintail cancellation prior to guard band insertion. Time-domain tailcancellation is achieved by subtracting a cancellation signal yc fromthe data signal yd, whereby the input reserved zeros are mapped in aninterleaved fashion to sub-carriers within the user's resourceallocation, and data symbols are mapped to the remaining subcarriers togenerate the time-domain data signal, and the time domain cancellationsignal is generated by repeating the last Nzt samples of the datasignal. During the interleaving of zeros onto the subcarriers, theinterleaving may be performed uniformly or non-uniformly.

FIG. 32 is a block diagram of a transmitter configured to performtime-domain tail cancellation prior to guard band insertion (OFDM)according to one or more embodiments, as similarly described inconjunction with FIG. 29. The transmitter illustrated in FIG. 32includes an interleave subcarrier mapping block 3206, which receivesmodulated data symbols and zeros in the frequency domain. The zeros arefirst mapped to the subcarriers in an interleaved manner, and the datasymbols are mapped to the remaining subcarriers. Thus, a subset of thesubcarriers that are uniformly interleaved over the subband is leftempty, for example, wherein data is not mapped to those subcarriers bythe mapping block 3206. Instead, zeros are mapped to the input of theIFFT block 3207 where these empty subcarriers are located and the datasymbols fill in the remaining subcarriers that have not been mapped toby the zeros. Thus, data and zeros are interleaved with each other atthe output of the interleave subcarrier mapping block 3206. For example,if eight subcarriers and two zeros are present, the input to the IDFT3203 may be [0 d1 d2 d3 0 d4 d5 d6].

The transmitter illustrated in FIG. 32 further includes an M size IFFTblock 3207, as similarly described in step 1 of FIG. 16, a tailcancelation block 3209, as similarly described in step 3 of FIG. 16, anda guard band insertion block 3210, as similarly described at the finaloutput of FIG. 16. Further, the cancelation signal comprised of thevector [−α −α . . . −α], is generated by repeating the tail part (alphavector) of the output signal of IFFT block 3207 N/Nzt times. The tailcancelation block 3209 generates the cancellation signal [−α −α . . .−α] and adds it to the output of the IFFT block (3207). In addition, acircular shift block 3214 (optional) may be provided to receive thesignal from the tail cancellation block 3209 to apply a circular shiftto this signal so that the N_(h) zeros from the tail appear at the head.That is, at least one zero from the tail portion is shifted to the headportion of the OFDM signal to provide continuity between consecutivedata symbols. Here, like numerals correspond to like elements and thefunctionality of each block is not repeated for conciseness.

Data modulation symbols are mapped to the M-IFFT block 3207, where asubset of the subcarriers that are uniformly interleaved over thesubband are fed with zeros by the subcarrier mapping block 3206. Lety_(d)=[y₀ y₁ . . . y_(M−1)]^(T), y_(d) ∈

^(M×1) be the vector at the M-size IFFT output, and y_(temp_c) ∈

^(N) ^(zt) ^(×1) the vector of the last Nzt samples of y_(d),y_(temp_c)=[y_(M−N) _(zt) . . . y_(M−1)]^(T)=α. The tail cancellationsignal y_(c)is formed by negating α and repeating it

$\frac{M}{N_{zt}}$times, for example, y_(c)=[−α −α . . . −α]^(T). The zero-tail signal iscomputed by adding the cancellation signal to the IFFT output asy=y_(d)+y_(c). The signal y has a perfectly zero-tail, for example,y=[y′₀ y′₁ . . . y′_(M−Nzt−1)0 . . . 0]^(T)

To reduce out-of-band emission of the OFDM signal, zeros may also beinserted to the head of y to generate y′=[0 . . . 0y′₀ y′₁ . . .y′_(M−Nzt) 0 . . . 0]^(T). One method of adding zeros to the head of thesignal y is to insert N_(h) zeros to generate y′=[0₁ 0₂ . . . 0_(Nh)y^(T)]^(T) ∈

^(M+Nh). This method will increase the size of y′ from M to M+N_(h).Another method is to create y with a zero-tail of size N_(zt)+N_(h), andthen apply a circular shift by the circular shifter 3214 to this signalso that the N_(h) zeros from the tail appear at the head. This methodwill not change the size of y′.

The next step is guard band insertion which may be performed infrequency or time domain guard band insertion block 3210, and assimilarly described in reference to FIGS. 17 and 18. It should be notedthat, in general, the tail does not have to be completely cancelled. Itis possible to partially cancel the tail by introducing a parameter thatcontrols the power spent on the cancellation signal.

As described herein, a method to generate a unique word (UW) OFDM signalby adding a UW in the time domain to the exact zero-tail generated witheZT OFDM, prior to guard band insertion, is provided according to one ormore embodiments.

FIG. 33 illustrates a zero-tail signal to be transmitted by atransmitter by introducing time domain samples with zero power or verylow power in specific positions of a time symbol tail. FIG. 33 furtherillustrates an insertion of the unique word according to one or moreembodiments. The zero-tail signal 3300 includes data blocks 3301 witheach data block 3301 having a zero-tail portion 3302 at the tail end ofthe corresponding data block 3301 and between two consecutive datablocks 3301, as shown. In addition, eZT OFDM supports insertion of adeterministic sequence, which may also be referred to as a unique word3303, on top of the zero-tail 3302. In one example, the unique word is3303 added to each zero-tail portion 3302 of the time domain signal, asshown in FIG. 33.

In general, the lengths of the zero tail 3302 and the unique word 3303do not have to be equal, for example, the length of the UW should besmaller than or equal to the length of the zero tail. For example, a16-sample UW may be added within a 64-sample zero tail. The length ofthe zero tail may be set as a function of the channel delay spread tomitigate the ISI while minimizing the overhead, while the length of theUW may be set according to synchronization requirements.

FIG. 34 illustrates a block diagram of a transmitter which adds UW inthe time domain to the exact zero-tail generated with eZT OFDM, prior toguard band insertion, according to one or more embodiments. Thetransmitter shown in FIG. 34 is similar to the transmitter shown in FIG.32, except a unique word is added by adder 3411 to the time-domainsignal y, and the guard band is inserted by guard band insertion block1700 or 1800 to generate transmitted signal x_(t). Blocks 3406, 3407,3409, 3414 and 3410 are similar to blocks 3206, 3207, 3209, 3214 and3210 described in reference to FIG. 32, respectively. Thus, likenumerals correspond to like elements and the functionality of each blockis not repeated for conciseness.

In another embodiment, the unique word may be added to the compositesignal after the guard band insertion.

Alternative approaches for tail cancellation are provided herein. In anexample, extending ZT DFT-s-OFDM to support OFDM, for either zero tailor unique word applications is provided. For example, FIG. 35illustrates a block diagram of a frequency domain guard band insertionblock of eZT OFDM, where a zero tail and zero head OFDM signal hasalready been generated by using approaches disclosed in one or moreabove embodiments. It may be seen that the block diagram of FIG. 35 isprovided with the ZT DFT-s-OFDM architecture. This shows that eZT OFDMmay be viewed as extending the framework of ZT DFT-s to OFDM. As shownin FIG. 36, eZT OFDM provides an efficient method to concatenate OFDMwith various DFT-s-OFDM waveforms. The transmission techniques of theseDFT-s-OFDM waveforms may be applied to the eZT OFDM signal after tailcancellation by the tail cancelation block 3609 and zero-head insertionby the circular shifter 3614. Other blocks shown in FIG. 36 (e.g.,interleave subcarrier mapping block 3606 and IFFT block 3607) aresimilar to those previously described, the functionality of which is notrepeated for conciseness.

eZT OFDM may support generating per-user signals with zero-tail and/orunique word. One or more embodiments provide a method for generating auser specific exact zero-tail and or user specific UW for an OFDMmulti-user transmission. In particular, FIG. 37 illustrates a blockdiagram of a transmitter (e.g., a base station transmitter) thatsupports multi-user transmissions, where k is the number of users,according to one or more embodiments. The transmitter uses the enhancedzero-tail mechanism to generate user specific exact zero-tail for DLOFDM multi-user transmission. Here, first the tail cancellation isperformed by tail cancellation blocks 3709 a . . . 3709 k for each user,then circular shifting is performed by circular shifters 3714 a . . .3714 k so that the N_(h) zeros from the tail portion appear at the headportion for each user, then a user specific UW is added in time domainper user by adders 3711 a . . . 3711 k, and then multiple user signalsare mapped to the corresponding sub-carriers of the full systembandwidth (BW) by using DFT blocks 3715 a . . . 3715 k subcarriermapping blocks 3716 a . . . 3716 k, and an N_(IFFT) size IDFT block3717, before the composite time-domain signal y is converted into serialdata symbols by a parallel to serial converter 3713.

FIG. 37 illustrates the MU eZT OFDM with frequency domain guard bandinsertion, where the guard band insertion is performed by using DFTblocks 3715 a . . . 3715 k subcarrier mapping blocks 3716 a . . . 3716k, and an N_(IFFT) size IDFT block 3717, as similarly described inreference to FIG. 30. For example, after the zero-tail and head isgenerated per subband, the signal is converted to the frequency domainby a DFT 3715 a . . . 3715 k of size M where M is the total number ofsubcarriers in the subband. Then, the output of the DFT blocks 3715 a .. . 3715 k are mapped to the corresponding subcarriers of the IFFT block3717 of size N_(IFFT) by subcarrier mapping blocks 3716 a . . . 3716 k,where N_(IFFT) is the total number of subcarriers in the system,including the zero guard subcarriers. Different subbands may havedifferent sizes as shown in FIG. 37 where M and M′ represent a differentnumber of subcarriers in the corresponding subband. When using timedomain guard band insertion, the signal per each subband is generatedseparately, and the oversampled signals belonging to all subbands areadded. It is noted that, in the uplink, the oversampled signals areadded in the air.

An alternative implementation of multi-user eZT OFDM is illustrated inFIG. 38. In this implementation, the data for all users are mapped tothe subcarriers via interleave subcarrier mapping block 3806 and N sizeIFFT 3807, a tail cancellation is applied to the composite signal viatail cancellation block 3809, and then circular shifting is performed bycircular shifter 3814 so that the N_(h) zeros from the tail appear atthe head. Then, guard bands are inserted to this signal by N size DFT3815, subcarrier mapping block 3816 and N_(IFFT) size IFFT 3817, assimilarly described in FIGS. 30 and 37.

A receiver structure is further described in reference to FIG. 23. Afterpassing through a multipath fading channel, the received signal may bewritten as:y=F _(NIFFT) ^(H) ΛF _(NIFFT) x _(t) +n  Equation 20where Λ is a diagonal matrix of F_(NIFFT)h√{square root over (NIFFT)}.It should be noted that since the tail is not exactly zero, expressingthe channel as a circulant matrix is an approximation.

At the receiver 2300, after passing the received signal through the FFTblock 2302 and sub-carrier de-mapping block 2303, the signal becomes:

$\begin{matrix}{r = {{B^{T}F_{NIFFT}y} = {{{B^{T}\Lambda\;{B\left( {I_{M} - {\sqrt{\frac{M}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{M}^{H}}} \right)}P_{d}x} + {B^{- 1}F_{NIFFT}n}} = {{{H(G)}x} + n^{\prime}}}}} & {{Equation}\mspace{14mu} 21}\end{matrix}$where:

$\begin{matrix}{{H = {B^{T}\Lambda\; B}}{G = {\left( {I_{M} - {\sqrt{\frac{M}{N_{zt}}}P_{c}F_{N_{zt}}{CF}_{M}^{H}}} \right)P_{d}}}} & {{Equation}\mspace{14mu} 22}\end{matrix}$

To calculate the G matrix, only the resource allocation and the lengthof the zero tail need to be signaled to the receiver. Based on thesignaled resource allocation, the receiver 2300 determines the datasub-carrier mapping matrix P_(d) and the FFT matrix F_(M). Additionally,once the length of the zero tail Nzt is known, the receiver determinesthe sub-carrier mapping matrix for the tail cancellation signal P, andthe FFT matrix F_(N) _(zt) , and thus it may calculate the G matrixusing equation 22 above.

The optimal LMMSE receiver 2304 may be used to compute the data estimateas:x _(est) =G ^(H)(GG ^(H)+σ²(H ^(H) H)⁻¹)⁻¹ H ⁻¹ r  Equation 23

For a channel that does not change very fast, such as an indoor channel,the LMMSE filter coefficients may be computed and used for a relativelylong time, reducing the complexity of the receiver.

One method to reduce the complexity of the receiver is to decouplefiltering with G from equalization. In this method, as a first step,one-tap equalization by 1-tap equalizer 2306 is used to computex_(est1=)(H^(H)H+σ²I)⁻¹H^(H)r. Then, in the second step, the dataestimate may be derived by filter 2307 as:x_(est=)(G^(H)G)⁻¹G^(H)x_(est1).

The performance of the disclosed eZT OFDM waveform has been analyzedwith simulations. In the simulations M is set to 512, and NIFFT=1024.Nzt is set to 256 and high delay spread channel is assumed. FIG. 39shows that eZT OFDM outperforms CP-OFDM due to the coding gain providedby the redundancy introduced as a result of the cancellation signal.

FIG. 40 shows that the out-of-band emission of eZT OFDM is much lowerthan CP-OFDM. Due to its low out-of-band emissions, eZT OFDM may be usedas an alternative to filter-based OFDM embodiments such as F-OFDM orUFMC.

Setting a length of exact zero tail is described according to one ormore embodiments. The length of an exact zero tail may vary from symbolto symbol or from transmission time interval (TTI) to TTI for the sameuser, and may take different exact zero tail lengths for different userssimultaneously, as previously mentioned.

The length of the zero tail may be set by changing the number of zerosfed at the tail of the DFT (e.g., the DFT 1601 in FIG. 16) foreZT-DFT-s-OFDM or the number of sub-carriers fed with zeros foreZT-OFDM. Optionally, the head may also be fed a non-zero number ofzeros at the DFT to further reduce tail power or out-of-band emissions.In this case, these will be in addition to the number of zeros fed toobtain a required tail length.

Mechanisms to generate unique word (UW) based waveforms both for eZTDFT-s-OFDM and eZT OFDM have been described above in reference to one ormore embodiments. Utilizing the disclosed mechanisms, the length of theUW in either of these waveforms may be altered as required by firstsetting the length of exact zero-tail to the desired length, which maybe equal to or less than a zero-tail portion of a data signal.

There may be one or more factors driving setting of zero-tail length.For example, the length of the exact zero tail required may be driven byat least one of several factors such as need for amount of delay spreadto be addressed in a given TTI(s) for a specific user, length of theunique word (UW) required for different purposes such assynchronization, channel estimation, phase/gain tracking, identificationof a specific user or a group of users based on UW sequence,beam-switching time, or any other purpose where the exact zero tail orunique sequence could be used.

Physical layer channels may be enabled on a per physical layer channelbasis based exact zero-tail. For example, length of the exact zero-tailmay be set differently for different physical layer control channels.This may be driven by a variety of factors. For instance, the beam-widthwith which each of the physical layer control channels need to betransmitted may be different, and hence may require different length ofthe exact zero-tail to compensate handling the required delay spreads.

The physical layer control channels may be transmitted with a widerbeam-width compared to the physical layer data channels. Even within thephysical layer control channels, the physical layer common controlchannel may be transmitted with a wider beam-width compared to physicallayer dedicated control channel. This implies that the length of theexact zero-tail to be utilized may vary from physical layer controlchannels to physical layer data channels and even within physical layercontrol and data channels, the lengths may be different.

It should be noted that this does not restrict the scenarios where thebeam-width or in other words same exact zero-tail length could be samebetween physical layer control and physical layer data or physical layercommon versus physical layer dedicated channels.

Additionally or alternatively, UW lengths may be different for differentphysical layer channels. A unique word generated from the exact-zerotail methods described above may also utilize the same methodology asused for varying the lengths of exact zero-tail. For example, the lengthof UWs may be different for different physical layer channels. Also, thelength of the UWs may vary from physical layer control channels tophysical layer data channels and, even within physical layer control anddata channels, the lengths of UWs may be different.

It also follows from the above that, even non-exact zero-tail basedwaveforms may utilize similar methodologies to vary their length as usedfor varying the lengths of exact zero-tail. For example, the length ofnon-exact zero-tail lengths may be different for different physicallayer channels. Also, the length of the non-exact zero-tail lengths mayvary from physical layer control channels to physical layer datachannels and, even within physical layer control and data channels, thelengths of non-exact zero-tail lengths may be different.

In view of the above, exact zero tail may be used for beam switching.Beam-switching is important in the above 6 GHz frequencies for severalreasons. It should be noted that this is a non-exhaustive list. Theseexamples could be because a specific user has moved, an existing path isblocked either by a dynamic blocker or due to self-blocking, a change inuser device's orientation, for example, rotational motion, etc., allpotentially leading to change in propagation conditions. It could alsobe because the transmitter, for instance, is switching between users, orbetween different physical layer channels, etc.

As the eZT waveforms described above produce exact zeros, the exact zerotail could be utilized to assist with beam-switching without anydegradation in performance. The exact zero-tail actually provides aperiod in which beam-switching may occur and the length of the exactzero-tail may be set or updated according to the beam-switchingrequirements. Details on how the length of the exact zero-tail may bealtered for both eZT-DFT-s-OFDM and eZT-OFDM are disclosed above.

Signaling for conveying the length of exact zero tail or unique word isprovided by the transmitter since the length of the zero tail or uniqueword should be signaled to the receiver. For example, the change of theZT/UW length is initiated by the mB and signaled to the WTRUs.

In one solution, the mB may use separate signaling for downlinktransmissions versus uplink transmissions. For downlink transmissions,the mB may use a downlink control information (DCI) format in thecontrol channel, for example, PDCCH or the like, to signal the new ZT/UWlength to the WTRU. An offset may be pre-defined and may be appliedbetween the TTI used for the control channel transmission, and the TTIwhere the new ZT/UW length is applied. Also for downlink transmissions,when the length of the ZT/UW is changed semi-statically, the length maybe signaled via RRC signaling or a Medium Access Control (MAC) controlelement (CE). For uplink transmissions, the mB may signal the change inZT/UW length to the WTRU, via PDCCH transmissions associated to uplinkgrants.

In another solution, the same signaling may be used by the mB toconfigure the new ZT/UW length to the WTRUs for both downlink and uplinktransmissions.

Both the disclosed eZT-DFT-s-OFDM and eZT-OFDM waveforms may be usedeither to generate exact zero-tail or to have unique word on a persymbol basis. These may easily be extended to adapt them on a per user,per TTI or any other combination thereof as these waveforms providefiner granularity at the symbol level to make required changes.

As described above, the addition of UW in both eZT-DFT-s-OFDM andeZT-OFDM is achieved in the time domain. Note that this may be doneselectively in only a subset of the symbols where in the other symbolsstill have exact zero tails for both eZT-DFT-s-OFDM and eZT-OFDM asshown in FIG. 41. The opposite could also be the case where most symbolscontain UW and few symbols contain exact zero-tail.

Without a loss of generality, it may also be seen that othercombinations where a subset of symbols have zero-tail (not exact zeros)and other symbols have exact zero-tail, subset of symbols have no tail(which would correspond to length of exact zero tail being zero) whereasother symbols may have different non-zero length of zero tails, andother combinations thereof are also envisioned.

UW may be utilized to convey scheduling/control information and/oruser/group identification. Unique word may refer to the insertion ofknown sequences instead of cyclic prefixes at the head of each thesymbol. This may be obtained by adding the unique word after exact zerosare created as described above.

Implicit scheduling for data channels may be implemented using uniqueword. For example, unique word or a part of the unique word may be usedto convey scheduling information for WTRU specific data channels. Here,a WTRU specific identifier or part of it may be used as a unique word inthe symbols carrying data for that particular WTRU. Alternately, theunique word may be generated by a function of WTRU specific identifier,or a cell specific unique word may be scrambled with a WTRU specificidentifier. Such a WTRU specific identifier may be assigned by the mBwhen the WTRU enters connected mode, for example, during a random accessprocedure. A WTRU may implicitly determine the data symbols destined forthe WTRU by monitoring the presence of preconfigured identifier in theunique word. In some solutions, semi-static part of the schedulinginformation may be signaled using a separate control channel for examplePDCCH which may last for one or more subframes. Such semi-staticscheduling information may include frequency domain resource allocation,transmission mode, MCS, and optionally the WTRU specific identifier tobe used in the unique word, etc. The fine grained time domain allocationinformation, for example, symbol level allocation, may be signaled usingWTRU specific identifier in the unique word.

Implicit identification of channel type may be implemented using aunique word. A WTRU may use a unique word or a part of a unique word toidentify or distinguish different types of physical channel transmittedby the mB. For example, the symbols within the subframe carrying controlchannel may be attached to a preconfigured unique word. A WTRU may bepreconfigured with a logical mapping between different channel types andan associated unique word. A WTRU may additionally determine the lengthof the control channel within the subframe by calculating a number ofsymbols carrying a unique word associated with a control channel. Such amechanism may be used instead of a separate physical channel such asPhysical Control Format Indicator Channel (PCFICH). Similar mechanismsmay be used to determine other physical channels like PHICH, etc.

A WTRU may identify broadcast channels similarly by monitoring forunique word reserved for broadcast signaling such as SIB, paging, etc.

A unique word may be used to identify a multicast group or a set ofusers. For example, a unique word or a part of a unique word may be usedto identify or distinguish multicast groups or different sets of users,for example, device-to-device (D2D) users. The symbols within thesubframe or an allocation may be associated with a preconfigured uniqueword. Users may be preconfigured with mapping between differentmulticast groups or user-sets and associated unique word(s). Additionalinformation related to D2D or the multicast group could also be deducedfrom the unique word or number of symbols carrying the UW. Certainbroadcast or multicast services, or different services offered forspecific D2D users may also carry preconfigured unique words.

The ZT and UW based waveforms could also use a zero head instead of thezero tail without breaking the cyclicity of the signal. In this case,time domain head cancellation is implemented such that an exact zero iscreated at the head instead of the tail. The cancellation signal isgenerated by repeating Nzh samples from the head of the IFFT output. Anexample is illustrated in FIG. 42 for DFT-s-OFDM, where the head thatneeds to be cancelled consists of the vector [Y1 Y2 Y3 Y4], which islabeled a for convenience. It should be noted that, in this case, Nh>Nt.

FIG. 42 is a block diagram which illustrates time-domain headcancellation prior to guard band insertion for DFT-s-OFDM according toone or more embodiments. The transmitter illustrated in FIG. 42 includesan M size DFT block 4201, a subcarrier mapping block 4202 and an N sizeIFFT block 4203, as similarly described in step 1 of FIG. 16, a headcancelation block 4209, as similarly described in step 3 of FIG. 16(except Nht time domain samples are used to generate data signal yd andcancellation signal yc to generate signal y), and a guard band insertionblock 4210, as similarly described at the final output of FIG. 16.Further, the cancelation signal comprised of the vector [−α −α . . .−α], is generated by repeating the tail part (alpha vector) of theoutput signal of IFFT block 4203 N/Nzt times. The tail cancelation block4209 generates the cancellation signal [−α −α . . . −α] and adds it tothe output of the IFFT block (4203).

Similarly, zero head may be generated for one or more embodimentsdisclosed above.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus. Some or all of the method steps may be executed by (or using)a hardware apparatus, like for example, a microprocessor, a programmablecomputer or an electronic circuit. In some embodiments, some one or moreof the method steps may be executed by such an apparatus. A block mayrepresent a processor or part of a processor for carrying out one ormore functions.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element may be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

What is claimed is:
 1. A wireless transmit/receive unit (WTRU)comprising: an antenna; and a processor operatively coupled to theantenna; wherein: the processor is configured to receive modulated datasymbols and zeros in a frequency-domain; the processor is furtherconfigured to map, in the frequency-domain, the modulated data symbolsand zeros in an interleaved manner to sub-carriers within a resourceallocation; the processor is further configured to generate atime-domain data signal based on the mapped sub-carriers; the processoris further configured to generate a time-domain cancellation signal bysign inverting and repeating a predetermined number of time-domainsamples at a tail portion of the time-domain data signal; the processoris further configured to combine the time-domain data signal and thetime-domain cancellation signal to generate an exact zero tail datasignal, wherein the exact zero tail data signal has a zero tail lengthequal to the predetermined number of time-domain samples; and theprocessor and the antenna are configured to transmit the exact zero taildata signal.
 2. The WTRU of claim 1, wherein the processor is furtherconfigured to generate the time-domain cancellation signal by invertinga sign of the time-domain samples and repeating a sequence of theinverted time-domain samples.
 3. The WTRU of claim 1, wherein theprocessor is further configured to generate the time-domain cancellationsignal by inverting a vector comprising the tail time-domain samples andrepeating the inverted vector a plurality of times to generate a stringof the inverted vectors such that the time-domain cancellation signalcomprises the string of the inverted vectors.
 4. The WTRU of claim 1,wherein the processor is further configured to generate the time domaincancellation signal by inverting the time-domain samples, converting thesign inverted time-domain samples into a plurality of frequency-domainsymbols, and mapping the plurality of frequency-domain symbols in aninterleaved manner to a plurality of allocated sub-carriers.
 5. The WTRUof claim 4, wherein the plurality of frequency-domain symbols areuniformly interleaved over the plurality of allocated sub-carriers. 6.The WTRU of claim 1, wherein the processor is further configured togenerate an exact zero tail data signal by shifting at least onetime-domain sample from a tail portion of the exact zero tail datasignal to a head portion of the exact zero tail data signal.
 7. The WTRUof claim 1, wherein the exact zero tail data signal comprises aplurality of data blocks each having a zero-tail portion, and whereinthe processor is further configured to insert, in the time-domain, aunique word at each zero tail portion of the exact zero tail datasignal.
 8. The WTRU of claim 1, wherein the processor is furtherconfigured to insert guard bands into the exact zero tail data signal.9. The WTRU of claim 1, wherein the processor is further configured to:sign invert the tail time-domain samples; convert the tail time-domainsamples into an inverted plurality of tail frequency-domain symbols withan Nzt size discrete Fourier transform (DFT); map the inverted pluralityof tail frequency-domain symbols to a plurality of allocatedsub-carriers in an interleaved manner such that another plurality ofzeros are inserted on $\frac{M}{N_{zt}} - 1$  consecutive sub-carriersof the plurality of allocated sub-carriers between each output of theNzt size DFT, wherein M is a number of the plurality of allocatedsub-carriers, Nzt is a number of the selected plurality of tailtime-domain samples, and $\frac{M}{N_{zt}}$  is an integer; and generatethe time domain cancellation signal by converting the mapped invertedplurality of tail frequency-domain symbols into the time-domain suchthat the time-domain cancellation signal is a replica of the invertedplurality of tail time-domain samples, repeated $\frac{M}{N_{zt}}$ times.
 10. The WTRU of claim 1, wherein the exact zero tail data signalis an orthogonal frequency-division multiplexing (OFDM) signal.